Did you get a pair of Rythmik's standard F8, dual driver subs? How do you like 'em?
.....Peter
I found a pair on the secondhand market - 30% off for a pair in piano black.
I like them a lot. FYI - the standard F8 uses the same amp and driver as the midbass F8 but allows the drivers to run lower. They are quick, match the SAM's perfectly, and are all I need for bass. However, I wouldn't think of them as subwoofers in the HT sense. They are better thought of as active bass modules. I imagine they are similar to your single-woofer modules, but with a bit more bass and a lot more headroom.
When I stack the SAM on top of the F8 I have a speaker that is very similar to the Salk Exotica 3 ($11,999/pair). They both have the same bass modules topped by high efficiency monitors (SAM in my case, Seas Exotica Monitor for Salk). I can run the crossover all the way up to 200hz, which fills in the lean range of the SAM. I'm using Nerf balls as removeable port plugs on the SAM.