Clip? That's kind of bizarre. Wouldn't mind hearing the diagnosis, once it is discovered. Please. Shit, man, don't give them ideas. There are things in life that cannot be unseen.
I have neither good nor bad things to say about Edirol -- looking at portable recorders, I'm not ruling out the Edirol for myself, whatever that tells you.
That's a good point about noise -- I actually had to "gain stage" my Mac/Duet/Singlepower amp in order to reduce distortion (I.E. the Duet was running too hot for the singlepower).
Another thing to try is to turn both up to full and see if you can hear any noise by pressing your ear up against the speaker (be careful not to accidentally play anything while doing this). Then turn one down and then the other to see which has a bigger contribution to the noise floor.
Well, if it sounds the same with pre at max vs. with the speakers at max (and then volume matched in both cases), then I wouldn't worry about it.
Remind me -- what's the setup? I'd say, set it so that it's easier to adjust the level on the one that's easier. (My quad 12L's are rather difficult to adjust -- I think I am going to take the advice to mod them to bypass their volume control, and then put a "real pre" in front of them.)
Impedance match.
Yeah yeah, I know, easier said than done, but I've been able to do it by ear, so it's not impossible. (Admittedly -- not in as complex a scenario as you have -- in my case, it was simply raising the level on the mixer [as a pre], and lowering the input sensitivity on active monitors.)
Is there a list of all headphones that have the HD580/600/650 style connectors? I know it's bass-ackwards, but I kind of wouldn't mind being able to browse said list. I can't seem to find my HD250-II's anywhere, and I think it's the only one I have left of that style. (I ran across it recently, so it's not completely gone, just haven't been able to find it since then.)