Would a Rythmik still benefit from an MBM?

[monomer]

I currently use Reference Infinity mains that can actually reach down to 27Hz (in-room response) and have an "original" VTF-2 (in 25Hz tune mode) with the 180-watt Class A/B amp and light-mass 10" woofer crossed at 50Hz over to a sealed MBM-12 that's crossed (@ reciever) at 80Hz. Both these subs are co-located and the blend is absolutely seamless. REW shows a relatively flat in-room response down to 21Hz and the bass sounds quick and tight and 'real'. I'm really happy with it currently yet I'm contemplating purchasing a Rythmik 12 (to replace the VTF) to get more extension but I don't want to lose any of the tightness in the mid-bass region or upset that seemless blend. Does anyone have any thoughts on this? Will I need to ditch the MBM? and maybe cross-over higher? keep the MBM and do a direct replacement with the VTF-2? SQ is everything, I don't care about flapping pant legs or vibrating my butt or getting slammed in the chest... I just want it to sound 'real'... so, which will sound better in the critical 50-80Hz region? My Infinities sound great in that region (better than the MBM even) but I really want to unburden the 10" IMG woofers in them to allow the best reproduction in the 80-200Hz range without interference from the lower freqs... and use the 350-watt MBM to bring those mid-bass freqs 'forward'. How will things change with a Rythmik 12? Thoughts?