I'm using a Teac CR-H220 to power them. The back of the unit says 75watts (I'm assuming that's max per channel?)
The reason I didn't go used is because I like to be able to hear something in person before I buy it. The used shops in my area have nice stuff, but they are extremely over priced.
I'm not sure what you mean by critical two channel listening. I have some experience recording with protools and a set of KRKs, but this is mostly for kicking back and listening. I accept iTunes for what it is. However, my entire library is encoded at 320kbs CBR. I can't tell the difference between 320kbs CBR MP3, FLAC or WAV, let alone the original CD. Ryan Adams' later albums are usually what I use to gauge sound quality.