BEST SPEAKER THAT COMES TO LIFE AT LOW LISTENING LEVELS

Best is Trial error adjusting base and tone controller in present set up until your satisfaction SQ. Zero cost

DeVore O/96 at low volumes are very nice.  The Lumin X1 is my preamp and has LEEDH processing which really does keep the music more balanced sounding at lower volumes...  That probably helps.

I have Magico A3’s mated with same subs as yours - Svs sb4000 and I am quite pleased. They are at your budget new but can be found used for much less. I have a db app on my phone and not sure of its accuracy. I set it at 60 db at my listening position. I can listen at that level but my 72 yo ears do not pick up all the nuances at that level. I have tennitis which I’m sure doesn’t help. I like it at 70-80 db. I have a dedicated room I can shut off so it doesn’t hinder the wife’s sleeping. Some have posted the A3’s are “dark”. I don’t find that the case at all. Of course cables make a huge difference in how and speakers will sound. I’m using Audio Sensibility signature cables that are quite revealing. Signal is via Innuos Zenith MK3 with Phoenix USB; USB switch with fiber optic. All interconnects are premium Audio Sensibility and Less Loss. I’ve not heard your DAC but I know DACs too make a huge difference in sq. I’m on #4 now and think I’ll stay awhile with the T+A DAC 200. There are better ones but, for the money, not sure. There are so many good speakers out there for your budget. Try to listen to as many as you can. If you’re willing to spend 15k, and don’t mind used, you can get speakers that retailed at 25-30k. And you’ve got power aplenty to drive almost anything. I’m powering my A3’s with 300 w, a Hegel H500. Happy hunting!!

You could try an equalizer or an integrated amplifier with a “loudness” button on it to amplify low frequencies at low listening levels. That’ll give you that rich sound at lower listening volumes. 

Since you have tried ML ESL hybrids, and liked them, why not audition a full range ESL, especially Quad 2912 and Sound Labs? I’m a Quad man, (ex ML - got tired of hybrids, YMMV) and I listen at such low volumes that my friends complain about it. So I guess that we have something in common there.

I can say from experience that Quad ESL’s work well with Bryston - I moved up to my own cost-no-object build, but Bryston still sounds good to my ears. Magnepan also fits with your 4B3, and might also fit well with your own requirements. I use a pair of 7B3’s for LF augmentation (Magnepan DWM).

And don't spend a dime on exotic cabling until everything else is exactly where you want it. Least bang for buck, most depreciation. IMO. YMMV.

Good luck!