Hi xnaron,
I still don't have a good answer for your issue. The first problem is I haven't been able to replicate it myself, testing on 4-5 PCs I have with Win10 and Win7. All my PCs have just worked, worst case was needing to install the SlimDX sdk, and not just use the slimdx.dll that I package w/ the plugin.
Only a handful of people seem to have this issue, some people I've emailed back and forth with had basically two identical PC setups, and it would work on one and not the other.... so... it makes my brain hurt
What I think I know so far is it is related only to slimdx not being installed or found properly in windows, and isn't at all related to xbox controller or its drivers.
I'll keep trying to think of the cause, and or come up with some other update.
regards
Eric