I sold my A40 headset but kept the MixAmp. I don't game much anymore but I gave BlackOps a brief run with the MixAmp going into my Audio-GD Fun's line in. I'd normally look down on double amping but considering I was using my HD650 I felt it would help.
The sound was pretty good. There's great impact in the bass and a reasonable soundstage but as much as I love these cans for music, I think you really need a headphone with exaggerated treble to compliment the Dolby Headphone decoder. I was rusty but with the positional queues giving me an unfair advantage I still managed to get a Gunship and dominated a game without dying. Good times.