I been trying out a couple of different op-amps inside my Gustard H10 dual channel sockets in combine with the 3x V5-OPA-D's that are inside the matrix M-stage dac and the two V5-OPA-S's that are inside the gustard H10. the 2 pair of OPA627AU's worked really good, but I didn't like the way the bass was as it was too punchy. The rest of the sound was ok. I just put in 2 pair's of AD797ANZ inside the H10 last night. Now I gotta use it for a while before I get used to them.So far i'm enjoying the AD797ANZ's. I really enjoying the Matrix M-stage dac, I didn't think i would enjoy it as much as the Gustard X12, but I enjoy it even more, I guess because I have a better control of the sound signature and I can change it at any time. While not having features that are useless to me that the X12 had and the weight of the money I had spent on the X12 on my mind.