I finally got all my switches working.
After contacting Opencockpits, their solution was to run SIOC on the Game PC as well and use the keyboard emulator built in to it. That didn't work either.
After scanning manu forums I found a script for AutoHotKey called AHKHID. This registered HID devices and displayed the data coming from them. Modified it severly and all the switches in the pit do what they're supposed to do - except the fire button (Hmmmmm). Think I may have had two problems.
Finally realised that when I'd been testing previously I'd had the controls in EECH set to keyboard. Since then I'd hooked up the BU8036 and and changed the controls option to that. I connected my trigger switch to the first button input on the BU8036 and can now blast away to my heart's content !!!!!!
Next stop - windscreen and projection.
PS if anybody want's a copy of the scripts for AutoHot Key, let me know.