Tube Pre and SS Power? Or the reverse?

+1 for the Tube Preamp / SS PowerAmp combo
I run C12000 with NOS tubes in the preamp, with 2 x MC611s to support the dynamic range, solid consistent power delivery you need across the spectrum.

I agree with @hilde45.

I have Revel f208 speakers which have the same sensitivity as yours. The impedance vs frequency is probably similar. 

I was looking to replace my old, venerable, recapped Mark Levinson #27 power amp with a tube amp. The #27 max power  specs: 100W into  8 ohms, 200W into 4 ohms and 350 W into 2 ohms. This indicates that the #27 has enough current available for complex loads such as the Revels (3.7 ohms at 90 Hz).

I tried several 60-120 W tube power amps but none really had the punch and solid low end, so I stayed with the #27.

I'm using a heavily modified Audio Research LS22 preamp. It replaced my ML #38s preamp. The ML 38s had no punch. Very bland. Big improvement with the LS22.

If the two subs are self-powered, then you've helped the power amp. If not, then tube amps might strain to create the power needed. 

My recommendation is to go with SS power and Tube pre. You'll need to size the power you'll need for your room. My room is moderate size (19' x 14'). The #27 is fine for this room size. You should definitely check out how the amp behaves for different loads.

This combination still has that tube warmth I crave (12AX7 in the phono pre (AR SP-6B phono) and 6DJ8 in the LS22).

Either all tube or all ss, I see no reason to mix. Unless you don't want to deal with many power tubes required for some serious power. But that Chinese stuff they now put in is available and relatively inexpensive, so it should come down to your speakers. If you do mix you will get a transistor sound, anyway. Makes no sense to me.

Tube preamp

Tube preamp and SS amp.

However, in my investigation into flea watt SET tube amp Sonics and some tube rolling, I’ll try to find a neutral preamp which will likely be SS.