You can run two 8 ohm cabs with an SVT, just buy a parallel 1/4" jack from rat shack (two jacks into one) and plug both cabs into the main output.
You can and I do all the time, 8 ohm cabs with parallel jacks are abundant. You can also run an SVT with an 8 ohm load if you're willing to risk the stress on the tubes/OT. I like to keep my amp happy and run a properly matched load so I don't run my SVT with my sealed 8 ohm 4x10. Sounds great with my V4 though...