ok... some progress maybe then.
right, so once the usb device redirects to the guest - do you see windows installing the usb driver? once it installs, then does it register itself as a COM2 device?
this might be the point in time when I need to start seeing the debug logs from the agent so I can see what's going on with usb...
(btw; lets stick with approach (1) for now - ie change com2 to com6. rather than the bios changes)