Moving from - de facto Reference gear - Quad to Martin Logan?

[Redux]

Martin Logans are much more full range but to get to more or less same level as old Quads you need to look at the top of the range selection IMHO.
Matching system components is critical as always..

By top of the range selection you mean Montis or summit X or even higher?

 

[MPS]

Quality is a very personal "feeling". Comparison between ESL-63 and ML products is bit difficult because Quad does midrange extremely well but have problems with low frequencies and high SPL. I haven't even heard the latest ML models but I expect the ones you mention to equal or better the Quad. YMMV.