so why did you settle on the AD826 duals?
To my ears. the AD8620 provides the best of everything; the bass depth, control and resolution trounce the other opamps, they provide mid-range performance on par with the OPA627/637, and have better treble extension than the others as well (air, soundstaging).
The OPA627/637s are good, but a bit "wooly", or perhaps "dark", in my opinion. They lack the detail of the 8620. The 825s were close to the 8620s, but lacked low-end control and resolution.
One thing to consider is that AD recommends a supply of 13v. I power my Bugle with two 12v SLA batteries and am very satisfied. I don't know how the Bugle would react with 8620s powered by a 15v DC supply. However, I'm sure regulating the supply to 12v is not an issue. Batteries can be had via eBay for $8 each. (Gruber Power).
FYI I modded my DAC as well. It came stock with the OPA2134. In the DAC, I much prefered the AD825s in a Brown Dog adapter. The 8620 was "grainy" in the DAC, while the 825s are buttery-smooth with no loss of detail.
Of course, the 8620s are pricey. I ordered up samples from BurrBrown and AD for my comparisons. Hagtech could not possibly spec the 8620s in the Bugle circuit as the cost would be prohibitive.
