I have the Adcom GFA-555 MKII. I got it used for $400 shipped.
I bought it for use with the Thiel CS3.6 speakers I got used. They are advertized as 4 ohms but dip down to 3 for everything over 100 hz.. my multimeter measures 3.5 for them. They're about 83-85 dB/1 watt/1 meter efficient. This is a combo that makes the Best Buy and Circuit City receivers cry.
First I tried putting my earplug headphones on and cranking it up to try and get the red distortion lights to go on. Then I tried an EQ where I turned everything down 10 dB over about 55 hz and cranked it up, then 20 so I could turn it even higher and get the same music volume with ridiculous bass volume. I tried this on many bassy scenes and parts in music.
I haven't heard any distortion, nor has the amp's lights told me it's distorted.
The axioms are almost 10 dB more efficient.. so unless you're deaf, this amp should do it for you.
