OK...thats a start.
1) Since HT isn't a priority, then there really isnt a need for too much attention in this area. However, IMO 5.1 music isn't as bad as some people think. The key is to have it setup properly, and have all six speakers working as one. It's a real eye opener. Just thought I'd throw that in there.
2) Small is relative. Are we talking 10x12 small or 15x23 small? The carpeting on the floor is ideal. However, you might wanna do something about those concrete walls. You'd suprised as to how much of your detail and focus is being destroyed by concrete walls. Just as with concrete floors, they're reflective. This can really make the sound screwey. As a suggetion, some people use artificial plants along the walls and in corners, to help with the reflection breakup. Some use area rugs on the walls...yep area rugs, to help absorb those harsh reflections. Some people use book cases with books and CD to help breakup those frequencies. IMO I would make this my next priority. Now granted, it is an apartment, so I wouldn't make this a renovation project. But I guarentee this is part of the problem with your detail.
3) Typical is another relative word. How close are your speakers to the walls? Considering your dealing with concrete walls, this is another think you need to look at. Speakers too close to the walls in general can cause issues, but concrete walls just add more problems. I got really good tips from rivesaudio.com on speaker placement. Check it out. Another suggestion would be to try setting up your two channel system diagonally in the room. I gave it a shot about a year ago and it helped to tame quite a few of my reflection issues.
4) Your sound quality and detail will come sooner that you think once you tackle those acoustic issues. Once those have been addressed, then you'll have a better idea of what your lacking in the quality area. Detail can been helped even without the upgraded amp. See #'s 1 and 2 above.
5) It's great that you are sticking to your main focus. To get the most from your speakers, you really wanna look into what's suggested above. You may not WANT to, but you'll spend far more money than you have to if you don't. Speaker placement is another big issue. Google rives audio and take a look at some of the pdf docs they have online. They will really help...a lot. Believe it or not, there is a science behind speaker placement. If it isn't done correctly then you'll never get to where your wanna be. But you always have to keep in mind what works for you. If exact placement isn't ideal, then you may need to consider some compromises. But in order to get to where you wanna go, you gotta start somewhere. Spending 2G's or even 5, for that matter, on an amp this early in the game, IMO wouldn't be the best move for you. Your system will do nothing but play what your lacking...even louder. The amp can add the detail and musicality your looking for, but only if some of those other factors have been tended to. Believe it or not, based on what you've said previosly, your listening to more room than system.
And you just never know, you might not need that huge amp anyway. You just never know. However, if it were me, I would wanna find out BEFORE I spend 2G's.
Like I said before, I'm no expert. But I have been in the same position as you to some degree. If I can help to keep your from making my mistakes then they weren't all for not. Just one mans opinion, but ask around!
Happy listening.