I have a extra copy of The Legaia I'm looking to unload and was thinking of listing it on eBay.

I'd list it here but I don't have the OBI for this copy so I doubt anyone would be interested.

But I was thinking... I shouldn't list this under "music", should I? Maybe under "video games > other" so it will show up with copies of the game? Since I don't have the OBI I was going to try and attract more casual fans, ones that wouldn't care about the OBI as much. If I went with music I think it would show up in a search for Legend of Legaia... but I don't think it would be as obvious.

What do others list their soundtracks under when posting them on eBay?

A lot tend to be under video games > other or video games > video gaming merchandise. So to have it seen it is probably best put in those categories, however, to avoid the insertion fee, some people will also put them under entertainment memorabilia or collectibles.  You do also sometimes see albums under music > cds but it is not as common.  I thought in the past at least, the final value fee they charge you varied by category, but that doesn't seem to be the case anymore, at least not with smaller items.  I have albums I'd like to list on ebay myself, but it was such a huge hassle on multiple fronts that I haven't been very proactive about it.  For buyers it's still great, but otherwise ebay keeps getting worse and worse...

I don't think it's even relevant. How many people actually browse eBay by category? They go there, search for something they want and browse a result query.

I remember eBay Germany had a specific category for game soundtracks (in video games, not music). Other localised eBay sites had it too, I remember.

But I haven't been doing a lot of eBay browsing these last 2 years and it seems A LOT has changed. Obviously gotten much worse, in every way.