Doug,

I believe you'll have no problem driving any type of headphone with the 2150, from the HD650 to K701's . I use the easy-to-drive HD 595's, and I am very happy with my listening experience.

I asked Scott before I bought my 2150 about the performance of the headphone output and how it was driven. I believe he relayed to me it is not driven directly from the amp and reduced via resistors like some are, so it has it's own amp.... but as gonk said it 's signal is from the preamp. He assured me the headphone output was inteneded to be as good as the rest of the amp, not just a "courtesy jack" .... as I pointedly asked him if it was.

Both volume controls can be used to adjust the volume... bass and treble work, the speaker EQ is defeated.

I can't say I'm an audio perfectionist, but I have my boundaries of what is "good sound".... and it does sound good! I am very particular about background noise though, especially using heaphones ..... and the 2150's headphone output is very quiet..... I'm quite happy with it

By the sound of your post you do not have headphones ? .... and you have a 2150 ? If you're wondering how low efficiency can will sound, the only way is buy 'em to try 'em. I bought about 5 different ones before settling on the HD595's. The HD5xx series are designed to deliver the sound into your ear a bit more directly than other headphones, and to me they deliver an experience unlike any other headphone. Wow , is all I can say..... and they're very efficient to boot. I never tried the HD650's because double cords drive me nuts, so I can't give you any feedback on those.

Wether the 2150 sounds as good as a $500 stand alone can amp is highly subjective and up to the listener. Before I tried the 2150, I was thinking I'd have to get a seperate can amp because all the amps and receivers I tried had noisy headphone amp sections. With the 2150 I have no need for one. Everyone's taste is different .