I use the Furman HA6 Headphone Monitor/Amplifier and it works pretty well, has 6 lines each with their own volume pot, and is expandable with their satellite modules that can do 2 phones per box. Multiple outs for the amps which can be separated or used as R/L. The only thing I don't like about the Furman is the sound the unit itself makes when it's on - it kind of whines a little.
I've used the Sony MDR V6 headphones for years and recently bought a Beyer DT102 (1 eared model of the DT100), and a pair of Beyer D770's. I think the Sony's might be louder but the Beyers isolate better, and the DT 100's have replaceable parts. The D770's are really MUCH lower in volume than either of the others, but the Furman can make them loud enough so far... The D770's also have much more bass response than either of the others...
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