Depends on if his boards are original, unlinkable games V Fighter/ Striker/ Lost World etc, came without the comm board. I'm fairly sure that linkable games do boot ok without the comm board.
Also twin boards won't link with deluxe boards, they need to be paired up.

If they are original and you have an extra rectangular pcb with 6 green led's sat over the back-up battery (the board is not showing in this picture for example - http://www.system16.com/boards/virtuafighter3tb.jpg) then maybe you just need the fibre optic cables, these are standard and can be brought from most hifi retailers etc.