I'm shopping for an amp to push my Polk SDA-1B's which are 4 ohms and,I think,good for up to 500 watts.I've got about $600.Am looking at an Adcom GFA-585,and was wondering about reliablity.Also i've noticed that there are alot of adcoms that come up for sale (Ebay) which leads me to think that perhaps these amps don't quite live up to their reputation for sound quality.Would appreciate your opinions on this amp and alternatives with output around 250watts 8ohms/450watts 4ohms.Thanks alot..John