Revel Gem 2 only goes down to 75Hz ?

Of course, that depends on what is meant by "rated down to." Some speakers are intended to crossover to a sub by design and are capable down to that point and others simply lack LF and the "rated down to" point is optimistic.

I have not looked at the Gem2 specs but I suspect they will reveal that they are in the former category.

It's not that simple... for example what is slope of the subwoofer and what's slope of the Gem2 crossover? The steeper the slope the quicker it rolls off... And what is the -dB at 75Hz? -3dB, -6dB, -12dB? Makes a huge difference...

I bet you'll be fine integrating the Gem2's with a good quality subwoofer

Sure. Integration will depend on the tools you have but I have no doubt it can be achieved.

Have you heard the speakers yet? I wouldn't worry so much about the specs. I may be mistaken but I really believe that some manufacturers are liberal with their specifications and after listening to some speakers I kind of have to wonder how they came up with the specs.

I think I found some specs on the speakers that you're looking at and, although they are only spec'd from 70hz up, the measurements on those speakers showed a low frequency extension down to something like 50hz at -3 db and drops like a brick from there.

My point is that you really have to listen to them. I'm running a pair of tiny Minuets. They have a claimed frequency range that starts at 55hz. I'm thinking that that's a bit optimistic considering that they have 3.5" woofers, but measurements that I've seen in reviews show that this isn't too far off from what they actually do.

In use, I usually cross my sub over at 60 - 65hz and it fills the low end out nicely.