I have an 880GA-UD3, and in my experiance, using a PS/2 splitter from the combo PS/2 port doesn't appear to work. (I suspect it isn't wired for it)
I also had to try 2 different USB->PS2 adapters, since the first one I used wasn't picked up by the board until after boot, so I couldn't reach the BIOS, the 2nd one I got works fine.
If Anyone does have 2 working PS/2 ports working from the Combo PS/2 port please do say so, so that people know if it is actually do-able.