The Revel Gem 2 is a sealed box, which means that its rolloff south of 75 Hz is going to be approximately 12 dB per octave. If you weren't using subs, you could partially offset that gentle rolloff with aggressive use of boundary reinforcement.
As for integration with subs, no problem. Either let the Gems run fullrange and roll off the top of the subs at 12 dB per octave, or roll off the bottom of the Gems at 12 dB per octave and the top of the subs as 24 dB per octave. I believe the latter approach is consistent with THX protocol. Both approaches use the inherent rolloff of the mains as part of the crossover filter. And even if neither of these options are open to you, you'll still be able to get a decent blend with a bit of tweaking.
Personally, I wouldn't design an octave of unneeded bass extension into a pair of speakers that were going to be used as satellites anyway, as you'd be paying an unnecessary penalty in efficiency and/or box size. I think Revel picked the right approach with the Gem 2.