Well the Magni is a great sounding amp, especially for it's price, and it does pair well with the HD650's. The HD650's are considered to be a "darker" sounding headphone with coloration, while the Magni is a bright amp. Pairing them together makes good sense. For me though, I prefer a darker sound and I like the warmth of tubes thus I like the Vali with the HD650's, and the $119 price tag for the Vali can't be beat for it's quality.
If you're in the $100 -$150 Range I suggest Magni for a brighter solid state amp, or the Vali for a warmer tube amp. If you have a higher budget then of course you'll have more options, but for the price of either one of those two amps mentioned, they are very good quality sounding amps with the HD650.
Magni is sort of bright to me too, but not bright enough IMO to change how the HD-650 normally sounds. I would say the Magni is still neutral with a hint of brightness. More than an O2 at least. I didn't find the Vali to be warm at all with my modded Q701 which is strange. It didn't seem to add any coloration, but with the HD-650 it did. Not sure why the difference. I probably will be the only one who doesn't like the Vali with the HD-650.
Chances are I'd love the Lyr with the HD-650. I would probably change it's stock tubes though to match it to my preferences. Maybe I can get it to sound similar to the Vali with the Q701
My favorite amp that consistently WOWs me with the HD-650 is the Headroom Micro Amp + Astrodyne. I can't think of any fault in any area. Been using it for 4 years now. With the HD-650 (and Micro DAC) it's very open/spacious sounding, very detailed and smooth. It doesn't make the HD-650 any warmer though. Maybe a little fuller mids compared to say how an HD-650 sounds on the O2. I guess the negative is that the HD-650 is not so laid back/relaxed with this setup (Amp still transparent sounding). Probably has more to do with the DAC. To me the HD-650 is capable of being very revealing. This wasn't apparent to me the first year of using the HD-650.
I got an iFi iCAN incoming any second and I bet it sounds great with the HD-650!
Edited by tdockweiler - 12/7/13 at 11:00am