Q? about sub out from my HT processor.

You are safe running the sub from the syb out on a processor - many people (when available) prefer to bypass the subwoofer's crossover availabilities and leave bass management to their processors to avoid cascading crossovers. A good amp would be a used sub amp from HSU. check out hsuresearch.com for new options.

Yeah, that LE-1 crossover/amp is pretty darned expensive. The people at Revel told me that the Sub15 wouldn't sound good without the equalization controls found in the LE1. Also, Revel recommends placing the sub in a corner to load it up, and using the LE1 to attenuate any overly reinforced frequencies.

I can't be sure of any of this and have to wonder how much of it is marketing. Any sub would be up against these same obstacles.

I would think an amp like the Bryston 7B would drive the Sub15 very effectively.

Higher frequencies will in no way dammage the sub! Your problem would be deep bass going to smaller drivers, or lower frequencies not being handled well by smaller drivers. But in your case, you'd never have such problems, even if feeding it a full range signal! If in doubt about crossover frequency of processors "sub-out", just call the manufacturer! Also, consult either Revel or the manual for specs and features. Not a big deal really...
Good luck