Hello Pete,
I'd have sent a pm about this, but I didn't see any way to do it. If I have missed something, my apologies. I attempted to use a game controller with more than 32 buttons with FSUIPC today, but didn't have success. There are two companies who manufacture USB game controllers with more than 32 button inputs, and I own one of them. The device I attempted to use has a total of 64 button inputs.
FSUIPC will use buttons 1 though 32 but not more. I'm expecting that in a situation where there is a POV hat, FSUIPC will use it, but this is not the case here. My suggestion/request is that FSUIPC have the ability to utilize more than 32 button inputs should a future version come out that addresses controller functionality. To that end, we can post one over to you to help further the effort.
Also note that there are some current titles which use devices such as this natively. Those are iRacing, Assetto Corsa, rFactor2 and DCS. There is also a remapping utility called SVMapper which will allow buttons 33+ to be mapped to keyboard keys if needed.
Certainly I understand that some things are a function of what windows gives FSUIPC :)
Thank you,
Derek Speare
http://www.derekspearedesigns.com/64-button-no-matrix-controller.html