No 5.1 output with MPC Homecinema?

This has really been bugging me lately...

I have a Logitech Z-5500 setup, and despite the fact that every other multimedia application utilises 5.1 channels by default (WinAmp, PowerDVD, WMP, DivX) with no issues, I can't get MPC to.

I've tried manually mapping the channels in the the Audio Switcher tab but that setting either seems to automatically reset itself or never work. I've tried fiddling with ffdshow decoder settings and reinstalling K-Lite, but to no avail.

I'm not terribly familiar with AC3Filter, but I tried setting the SPDIF passthrough for everything (MPEG Audio, DTS, AC3) and made sure the output format was 3/2+SW 5.1 Channels, but still no dice.

Any help greatly appreciated folks.