I listen to mostly classical also, so I intend to build Rhythmik OB wth GR Research paper cones. 2 or 3 per side. OB will minimize acoustic problems in bass freqs. I do wonder how detailed the Rhythmik amp is.
My friend had a single ACI sub supporting Piega C8, it was excellent synergy with that very fast speaker. I don't know how much detail was missing because I was not familiar with the music played. ACI has infinite phase control which really helps. I adjusted that a little and found a big improvement. Now he has two ACI Titans so I wanna go hear them and help him dial them in all the way.