Anyone know what's happening when one of the two variable signal levels are chosen in the M-Audio Delta control panel (hardware settings tab)? Is the signal being digitally boosted for the "Consumer" setting, or is it being digitally lowered for the -10dBV setting?

Edit -- RMAA seems to think it's being digitally lowered for -10dBV (output levels too low with a loopback except at the "Consumer" setting).

Those settings were implemented for level-matching when using a Delta 410/1010 (8 analog outs) with different gain power amplifiers/monitors in surround/multi speaker pair applications.

What they actually do is decreasing the op-amps output (peak RMS voltage or whatever) so it's not digital but analogue attenuation. Does not create any audible problems/issues.

Exactly ... Studio equipment often operates at lower sensitivity with higher output voltage so your soundcard's analog in-/outputs can be adjusted to match either consumer or studio (professional) equipment ...

I wonder if that could cause a change in sound, used in conjunction with an external headphone amp or other amplifier (either for the better or worse).

I'm surprised it would/could actually change the output of the op-amp, is there a mechanical or electronic relay of some sort on the card controllable via software?