MBL 101 (~1990) - amp suggestions.


Does anybody have experience with those speakers:
Designation was MBL 101, or MBL 101a/b/c (letters may designate colour).
They have _no_ cone drivers, only three 'Radialstrahler' units, the same size units as in later/current MBL 101 range, but lower crossover points. Subwoofers (MBL 201) were optional, I do not have them.
So far I have tried the following amps:
Pass Aleph 4: almost there, but feels like lacking authority. Also, female vocals seem to suffer (males fare better).
300B SET (glasshouse/hificollective): they make sound, even loud if pushed (circuit allows 300B to go A2), yet the match is poor, orchestra becomes a mess.
Moderate power SS AB amp ("INnovative Audio Ultrapath"): pointless. Sounds flat and gutless, worse than Aleph 4 or SET.
Mark Levinson 23: the best match so far. Controlled and effortless; merciless at times (poorer recordings are exposed for what they are).
-- Do you think I can [substantially] improve over ML 23?

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I heard one of these models with a pair of CAT monoblocks and it sucked them dry. Even at low volumes you could tell that these amps werent nearly powerful enough. Perhaps atma-sphere is correct, although I have my doubts, that it is the type of the tube amp. 
I will go active in bass and relieve MBLs from 100 Hz downwards: my 101s are super old and have no bassreflex box, which current 101s have; MBL themselves suggested pairing with their active MBL 201, but I will try home-made dipoles instead (I find room modes and booming ported box bass rather dilsturbing, reproducing bass that way does not recreate classical concert or opera experience too well).
I might be jumping to an obvious but wrong conclusion, But I think open baffle subs would be quite compatible with the MBLs.
- Just to clarify “would” or “would not” be compatible?
I like spaciousness of MBLs a lot - they just fill the room. However, they excited vertical room mode, Even with that caveat MBL bass is ok.
Then Gradients showed me that bass can be more tuneful - I am currently using Gradient 1.5 Helsinki, cardioid mids and highs with dipole below 200 Hz. There is a bit of placement difficulty (easy to get decent stereo image, but difficult to get optimal bass), but once in position I like the overall sound quite a bit, I just wish I could have more uniform sound in the room - like with MBLs. With clean dipole bass - like Gradient. Gradient 1.5 have one 12” driver per side. Seems barely enough. So I got something bigger (two BMS 18N862-8 per side).