I'd like the full panel to be 2 joysticks, 8 buttons (16 total) with a trackball and two spinners. Can that be wired properly on the Ultimate I/O?
A trackball and two spinner setup needs 4 optical axes.
AFAIK the Ultimate I/O will only handle 3 optical axes, so by itself, it's one axis short.
When you order the SpinTraks, get one with USB and one without.USB.

Pretty sure the USB interface is the same one used for the
U-Trak.
Here's the pinout.

Each optical axis needs:
5v operating voltage
Ground
Two data lines
- X1 and X2 for X-axis or Y1 and Y2 for Y-axis.
- If the cursor moves in the opposite direction expected (i.e. turn spinner right ==> cursor goes left), swap the two data lines.
Scott