In few days I will recieve my Matrix M Stage (HPA-1) USB to power my Senn HD650.
I think it's a very good amp for beging with and I will use it at first on stock mode and later I will make any modification on the opamps.
This post it's soo huge to read with no time and for that reason I ask if there any particular recomendations to DAC's opamp and amplifier opamp (besides the expensive Opa627).
Thanks to all.
LME49720HA or LM4562 would be a good start.