Damn, James-F, you're right about the CT1703-T being a noisy POS.
I just got a CT2770 SB16 Value (CT1747 chip) and it came with a CT1703-T, and it hissed like crazy. Replaced the chip with a CT1703-A taken from a dead AWE32, and the hiss was cut by 50%. Now only the PCM volume slider hisses when I don't mute it.
Looking at the op-amp section, there's a corner of the TL074C that is left floating, which is a *huge* no-no. I'll terminate that uncommitted op-amp and see what that does for noise.
Update: Terminating the op-amp still didn't totally get rid of the PCM hiss, but I feel better for having doing that so I'll leave it terminated. I suspect that, at this point, it's a combination of too high gain someplace and generally poor layout and circuit design that's causing the hiss. It does sound much better than how it did at first, though.
Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁