I connected my Audioengine A2+ speakers to my XPS 8930 PC using a USB connection to bypass the integrated sound card (the A2+ have a built-in DAC) AND connected my subwoofer to the #10  port (the "Center/subwoofer LFE surround" port) using a standard mini-jack audio cable.  The A2+ speakers sound great, but there is no sound output from the subwoofer.

I also tried connecting the A2+ speakers to the #8 port (the "Front L/R surround line-out" port) using a standard mini-jack audio cable and leaving the subwoofer connection as before. Again, the A2+ speakers sound great, but there is no sound output from the subwoofer.

I tested the #10  port using the configuration feature in the Playback tab of the Control Panel\Sound panel, and got a successful test of the subwoofer and the connection. It was the configuration for the AvSoft Virtual Sound Device, because the subwoofer does not show up in the configuration for the A2+ speakers.

Any thoughts?