ASUS drivers are ..passable at best let's say. It's best to leave everything off

And yes you can make those adjustments, but the only thing I would play with is the EQ...every "enhancement" sound terrible.
I'm just gonna say that I have the D2X and it's a great card by its own right. I replaced my prelude with it before for the same reason that I didn't have any PCI slots available...and to be honest, I consider the d2x pretty much equal to the prelude for most parts.
The Auzen HT HD is also a great card, and is MUCH more versatile than the d2x. The only reason I haven't tried it is..well I spent my money on a STX.
also I wouldn't get so riled up in OPamp choices tbh. Most of them will color the sound slightly, but I would say most consumers don't even care.