That is a nice set of speakers! I have the LS50's and love the sound of them, I am guessing the Ref 3's are spectacular. Having gone through some upgrades in amplification with my KEF's, I would say that you could find some significant improvements trying some other gear. My original amp was an NAD 375BEE integrated which sounded great and provided a deep well of power for the low sensitivity LS50's. My eyes opened up when I bypassed the preamp section of the NAD integrated with a Schiit Freya+, it was a significant improvement. I later replaced the amplifier with a Coda #8, again a very significant improvement.
I am not advocating for these products, and in fact I am in the process of auditioning replacements for the Freya, but just saying that I think you can do better with a speaker of that quality. The M33 looks great on paper, but like every Swiss army knife solution, I expect there were compromises made along the way. The fact that you are not getting the bass you want, and you are still missing that certain something tells me you should shop around.