"Now I've decided to slowly build my system...the amp is just the first step. If I get the A21, the P7 will be the next piece, followed by a new source, and finally cables."
I don't know if I did a good job explaining my point in my first post. You list some specific qualities that you want your new amp to have. Setting goals is excellent on your part. Very few people actually do that. I'm just questioning how you are going about this. When I say you need to build a system, I don't mean that you need to buy everything at once, but just have a clearly defined path. At the very least, you need to hear your speakers with the A21 and P7. Otherwise, its just a coin toss. Its more work, but I would say that you really need to hear the combo before you purchase.
One other thing I see from reading your posts, is that you seem to be favoring the amp as the more important piece, as opposed to the preamp. I won't tell you what to think or how to spend your money, but I would highly recommend you treat the preamp as the more important of the 2. As long as whatever amp you get has enough power to drive your speakers properly, the preamp should make a bigger difference in terms of sound quality. If you skimp on the preamp, you're just going to start fooling with cables, tubes and other various tweaks. By the time you figure out what's going on, you'll have spent a lot of money. Not getting the right preamp has to be the biggest and most common mistake in audio.