Just got a headset with external 7.1 surround sound, 3.5mm jack to external DAC module to USB at the computer.

I can select analog 7.1 surround sound, and all the channels except the subwoofer one respond correctly. When I go to adjust the subwoofer slider, all it does is mess with the rear right channel, and it's leaving a lot of bass out.

How do I make the subwoofer channel active and recognized?

-SOLVED- (more or less)

The trick was disabling 7.1 on the dedicated DAC, then letting the OS handle all the work, with the realization that for my headset, that's where the 'subwoofer' would be sourced from and it's working better that way.