A few quick comments about the Constantine. Please realize I have neither a Pardisea or a Constantine. The suggestion of swapping the OP2107 for an OPA2604 in the Paradisea is a no brainer, assuming the rail to rail voltage is 36volts or less [which it is (+17)-(-17) = 34 ]
In my experience, everything an OPA2604/2134/2132 can do, the OPA2107 does mo betta. Its going to have a similar 'BurrBrown' sound signature, but with better resolution, more extention and cleaner.
The Constantine uses a Analog Devices AD826, and it has that stereotypical AD sound, not particularly warm as is typical of the BB chips. Its rated for a maximum of 30volts rail to rail, so if MHDT Labs has followed specifications, swaps for other non AD chips discussed here are not going to be problematic. If you substitute a OPA2107 for the AD826 you're going to get subjectively a much 'warmer' sound, and if one were to listen blind, one might guess the Constantine has a tube within. I happen to like that sound, but others might prefer the more stereotypical 'cleaner' AD sound. In that case, I'd suggest the National LM4562 which was suggested by Legarem for the Paradisea, but wouldn't raise voltage concerns in the Constantine, given the constraints of the extant AD826. I have directly compared the AD826 to the LM4562 in my own Zhaolu dac, and much prefer the later, finding it more extended and neutral, with nary a hint of grain. But the difference is not going to be as large as a swap for an OPA2107.
FWIW, I had 2 OPA2107 and a single AD826 in my Zhaolu for about two weeks. I finally decided I couldn't live with it, as it frankly put me on edge. I presently have those same 2 OPA2107 in the same positions, and a LM4562 in the position previously occupied by that AD826. Its been there for the last 2 months and I feel no motivation to change it.
This is a subjective call and YMMV.
