Pete, do you use a separate high pass crossover control for the F8 mid-woofers, and if so, where do you set the frequency cut-off? I'm just curious how you blend the mid-woofers with the SAM XRS since they seem to have a fairly broad frequency overlap and the mid-bass from the SAM XRS should already be quite good. In my room, my "regular" SAMs only need a touch of weight in the 30Hz-50Hz range hoping to fill in with subwoofer(s). My system is for music only and I mostly listen to jazz, blues, and folk music, and occasionally classic rock.
The mid-woofers go from ~60 down to 30Hz. My subs from 30 down to 14Hz. All by ear. I set the upper frequency by starting higher and reducing until any muddiness from too much overlap. I have REM with mic and all, but have been too lazy to do objective measurements. The Rythmik mids and subs are incredibly clean, fast, and defined, so very little bass bloom, boom, etc.
Oh... almost forgot and very material: I have plugged the ports in the SAM HO's. When listening to them alone (without bass foundation), I find plugging the port tightens up the bass dramatically. That raises the low end response frequency though. But with the midwoofers, that's perfectly fine.