I can certainly make some recommendations. Just remember three things:
1) A lot of gear is very personal. What sounds good to some people might sound like shit to another person. I've had to resell quite a few pieces over the last couple years.
2) A lot of gear is hyped by shills, either fanboys or people in the industry. Don't believe everything you read. It is why I consider the headphone communities a toxic online environment (and the higher end home stereo forums seem just as bad).
3) Your source feeds the DAC, the DAC feeds your amp, the amp powers the headphones or speakers. There is always synergy between those four parts. Sometimes units will combine these four parts. A CD player, for example, traditionally handles both the source and DAC parts. There's also a lot of trial and error and no true "right way" to do things. If you find something that works, stick with it. But one thing I've learned is that if the headphone does not sound good, usually it is an indication of a problem with the source.
I favor these guys: https://mrspeakers.com/shop/closed/mad- … ort-strap/
It's a mod of an existing headphone, but a very good one. They handle any type of music I throw at them, are comfortable and are not picky with amplifiers. I've had the chance to listen to some of the more megabucks headphones (Audezes, Hifiman) and I think these hang right in with them. I ended up getting one for work and I liked them so much, I bought a second pair for home.
The HD600 and HD650 are amazing audiophile headphones for their price tags (both can be found for under $300 with some light searching normally). A lot of people end up seeing them as a starting point and then end up sticking with them. They're stood the test of time pretty well.
You can rent high end headphones from these guys: http://www.thecableco.com/Product/NEW-H … ng-Library
I recommend the Schitt amps: http://schiit.com/products
They out-perform their price by leaps and bounds. I have a Magni, Valhalla 2 and the original Lyr. The $100 Magni is frighteningly good for the price and will drive pretty much anything. It's slightly bright, but that pairs good with the Mad Dog IMO. I was able to score the Valhalla used and I use it for my HD600. It is an OTL amp (directly driven by the tubes), so it specializes in driving the HD600. It struggles with the Mad Dogs though (Mad Dogs are orthodynamic, which means they need a lot of power pumped into them, especially for bass control). OTL amps can't feed them that.
The Lyr gets the most work from me at my work place and I use it with the Mad Dog. I had to do some "tube rolling" with it to tweak the sound (long story, but basically I'm using 1970's Russian Voskhod 6n23p tubes in place of the tubes that come wit the the amp). It gives a BIG, lively sound to the music.
Schitt gear holds its value really well. Usually it can be resold for about 80% or more of the cost if its kept in good condition. I feel like it's hard to beat these amps without spending a ton of money and getting into the multi-thousand dollar range.
This is where I run into problems with digital audio. Admittedly, I'm still in the experimental phase and there really isn't a highly agreed blockbuster solution. A lot of people use their computers and they run the audio out from a USB port to a separate DAC that has a USB input. The problem with this is computers produce a lot of noise and that affects the digital signal that gets converted. It's where digital sound gets that harsh, analytic reputation (as opposed to the "smoothness" of vinyl). Schitt offers their Wyrd "USB decrappifier" to help, but I'm not really confident in USB audio yet. I'm always interested what people's individual solutions are.
I view the source and the DAC as necessary evils. That is, once you get something together that is serviceable, you can tweak the sound with the "analogue" parts of the rig better (the amps/headphones). But if you're feeding the amps/headphones crap, they will reflect it in their performance. A $2000 headphone powered by a $6000 amp can't sound sound good if it's being fed crap. This is where vinyl kicks digital audio's butt, by skipping the whole conversion from 1's and 0's and any associated issues.
At work, I use this: http://www.amazon.com/iBasso-DX50-Maste … B00J6RVQJM
It has two ports at the bottom. One is for a regular iPod-style headphone jack that is driven by a small portable amp. I almost never use this, because if you feed it into an amp, you're "double-amping" (people tend to do this when they hook their phones into the Aux jack in their cars). The other (the line-out) is designed to feed into an amp and comes directly from the DAC inside the unit (using a Y-cable) So basically, I control what goes into the Lyr via the unit. I also installed Rockbox on it, which is leaps and bounds ahead of the stock firmwares (iBasso never figured out how to stop their firmwares from altering the sound on the units, Rockbox fixed that, so it's outputting a pretty neutral sound across the spectrum). The firmware navigation is clunky, but it works. I also use it in my car, again, much like people using their phones with the Aux jack to play music, except I'm just using a regular 1/8-to-1/8 cable from the line-out.
It doesn't get a lot of love from the audiophile community (Ibasso has always had a slightly tepid response to their gear) and admittedly, if I knew for sure something would work better, I'd upgrade. But for the price and convenience, it's hard to beat. Prior to installing Rockbox though, I nearly gave up on this. It's also pretty rugged: I pretty much beat the hell out of mine on a daily basis and have had zero issues with it.
At home, I'm currently using this: http://www.amazon.com/Sony-HAPS1-Hi-Res … ony+hap-s1
Jack of all trades, master of some. The headphone port isn't so impressive (I haven't tried running the speakers from it either) but for a file browser and something to handle the digital-to-analogue conversion, it's top notch. In the audiophile community, it has one achilles heel: You can't use an external DAC, you HAVE to use the built-in DAC. For 99% of the human population and for audiophiles that are fine with sigma-delta conversion (another long story), this isn't an issue and I think it sounds damn good. The computer uses an app to transfer songs and it can be controlled via remote from a tablet or smartphone. Again, not cheap, but incredibly versatile.
Another solution is the Olive One. http://www.myoliveone.com/Ones/tech_specs
I've had my eye on this for both the looks and the digital output (which lets you connect an external DAC). It's newer and there aren't a lot of impressions, but it falls right in line with what the Sony does. Has lots of potential, especially when there aren't a lot of options out there.
If we're using CD's, I recommend a player that has SPDIF output. A CD player has a built-in DAC and a lot of them simply aren't very good. SPDIF means you can use the CD player as a straight transport and have your separate higher-quality DAC do that conversions. There are a lot of bad, consumer-grade CD players out out there that either have movement in the CD tray (causes jitter) or bad DAC implementation and I believe that is where digital audio gets a bad rap. I used to have a pretty nice player (Marantz SACD-8004), but I sold it to fund the Sony file player.
One last thing: Upgrade the power cables and interconnects from the stock ones on any gear you pick up. The stock ones tend to have a bit of that "digital harshness" you want to remove. Nothing fancy is needed (so no $1000 power cables or $500 RCA interconnects that people rightfully poke fun at), but a pair of $50 RCA interconnects and a copper power cable in the $80-$100 range are good enough to clean the sound up. This is a hot topic that many flame wars have erupted over in the audiophile boards. For me, the difference was very noticeable (in a good way)
tl;dr Digital audio is a huge pricey pain in the ass with a ton of variables, but worth it once you find the right combination of stuff.