Well for one, Radeon cards don't use SLI, they use Crossfire, but that mainboard doesn't support SLI since it's not an nvidia chipset. I also don't see that it supports Crossfire, as only some Intel chipset boards do that. So there is no way he's going to be able to connect the two cards in such a way that they can both feed a single display with one cable.
The FireGL does not support Crossfire connectivity either. Even if the board and cards supported Crossfire, there wouldn't be a way to make it only use one card's capabilities at a time but always feed through a single cable, the way you're thinking of. I don't think you could use a FireGL in Crossfire with a Radeon anyway.
It is possible to use them separately most likely, but yes, if he's only got one cable and one input to the monitor, he'll have to swap the cable each time. If he gets a monitor with dual-inputs, he may be able to just use two cables and switch back and forth, but that will mean most likely that one port is DVI and one is analog VGA.
A switchbox could be used if the monitor only has one input.
Unless he REALLY specifically needed particular features supported by the FireGL drivers but not by the Radeon, the Radeon ought to be good enough for most graphics work. The GPU used is in fact
identical to the Radeon GPUs, they just modify the drivers and the PCB a bit.
