Question about Revalver

It's probably about what sounds the best, but when you use just a preamp-out, you'll only get a preamp signal. In that sense it makes most sense to use a power amp emulation too. But most people don't use poweramp emulation before an impulse, so... Test and see what you like the most.
 
I'd say it depends on how the impulse was made... most people run the sweep through the poweramp of their amp, so that tone shaping is included. I don't; I use a flat SS poweramp. But like Torniojaws said, it all comes down to what sounds the best with your setup.