I've edited my last comment a couple of times, so there's a couple of extra ideas to check.
Sounds like your wiring it up correctly. Yes, it's a single mini jack to twin RCA on the amp. Make sure that windows and the amp are both set to 5.1. I honestly think that you might be getting a signal but it could be down to the volume levels. Amp test signals are normally quite loud though I've no idea what frequencies they use.
I'd unplug the buttkicker (or at least turn it's amp off) and then creep the simhub/pc and amp levels up to see if anything comes through. Make sure you bring the levels back down before using the BK again.
Also check that you're definitely selecting the correct source on the amp
Its working at the moment. I think its something with the Sony amp.
What is a good alternative for the Sony STR? I have 4 transducers right now, but maybe I'll replace them for bass shakers. The Sony has too much settings to. I want something more simple.
Thank you Brutal for your help so far!