What would you buy

great advice to call Johnny Rutan, he can take you thru various options to make your Two’s sing. The acoustic couple on the rear plays pretty low and needs to couple with wall..and IMO requires an amp with some grunt and damping factor to control it.

IF your Rogue has pre out/amp in you can use Vandersteen high pass filter and a Vandersteen model 2 ( a pair used ) or one Model 3 sub w 11 bands kf analog bass EQ.with that setup you take load off main speakers and amp and get same transfer function to both subs and main. 

have fun enjoy the music.

 " The Rogue doesn't have an output for a sub woofer."  The Rogue does have a subwoofer output!

Used Octave V70se or 110se. I know a dealer you can probably get a good deal from. Great bass like ss. 

Johnny used to sell the Music Reference RM-9 to 2C owners, a marriage made in heaven (owners of that pairing live happily for years). Alas, the amp is no longer available, and is hard to come by used. The RM-200 might be even better with the 2C, as the amp likes low impedances more than does the more traditional tube design of the RM-9. RM-200 Mk.2's can occasionally be had for around $3,000, the original for $2,000. Worth waiting for.

Watts are watts, doesn’t matter how they are derived.  The tube amps clip much more gracefully  and that is the reason they sound more powerful.

Then why did every one I tried sound more powerful even when driven nowhere near clipping? Three different solid state amps, 150 to 200 wpc, the best of which was the McCormack DNA1, but with less dynamism, mass slam and control, than 50 and 60 wpc tube amps. 

Its not true in every case. There are anemic sounding tube amps, just as there are POS SS. Its probably more the transformers than the tubes but whatever, point is, they are so not the same its actually kinda odd to be having an argument about it. I mean heck not even all SS watts are the same. They sure don't sound the same. Everyone knows it. Amplifiers sound different. Your position is simply untenable and only goes to show the hole you can dig yourself into when you rely too much on tech talk.

Vandersteens at 86 dB are admittedly at the bottom of the range of suitable speakers. But that's the bottom of the range of suitable speakers, period. Because sound is logarithmic, the power needed to produce it increases exponentially. Not linear. Its a big mistake ever to buy a speaker this inefficient in the first place. But if you have one, still its better to drive it with watts that sound good than watts that don't.