Multi GPU's

I've finally been getting to put my hardware to use and it seems I'm already hitting my head against a wall. I've just been messing around with cycles to see what I can do. Here's the problem... I've got two 560 ti's and they do seem to work well, until I crank up the geometry for light to bounce off of (cycles). Once I put the scene in a dome (actually I'm just using a huge sphere) the whole thing shuts down.

Is there a correct way to use multiple gpu's? I've heard that it won't work with SLI enabled, but I already proved that one wrong. It works fine either way. Once I use a dome it crashes. All I wanted to do is get a more realistic lighting effect going... or so I thought. Any thoughts?

Specifics:

i7 2600k 3.4 ghz
8 gig DDR 3 1600 mhz
Geforce 560 ti 2 gb x2 (with and without SLI)
Raid 0 SSD's
Win 7
Blender 2.63a

I'd love to upload the blend file, but I'm going to need help for that... really not sure if it would help unless someone had the same computer maybe?

I did get it to render, but it was before I realized that I didn't have the dome in the scene. Once I tried to get that to render it was crash city!

Figured it out... kinda. Looks like it's really not a multi GPU thing at all. I was trying to use what amounts to a sky dome and cycles didn't like it at all. Too much bouncing maybe? I don't really know. All that I do know is that I popped the top off and it worked just fine. Wierd thing is that I tried raising it off the ground plane about half the hight of the monkey head and that didn't work either. There's some kind of relationship with the amount of open air and cycles that has to be met or the thing (at least on my machine) crashes.

Forgot to add the end result... not great, but I'm having fun!![You must be registered and logged in to see this image.]