Interesting idea, and one that could work. This is far from an urgent project though (just floating some ideas about, really), so I won't be rushing into anything. As usual, when I've decided to go ahead, extensive research will be undertaken, and the processing of as much relevant info as possible will be carried out before a choice is made.
Yes, so they say, and in certain circumstances that may be true.
However, I've used umpteen different passives in my system with the Copper amp, which is even more sensitive than a Quad 306, and high-efficiency speakers (95db Tannoys), and where on paper a passive should thrive, yet (aside from LDRs), when used the soundstage collapses and they *always* sound soft/veiled/'padded out'/lacking in 'drive' and dynamics (even receiving a 2v digital signal),
*in comparison* [that bit is crucial] with the best active designs.
Therefore, given the above and the type of system I've tried passives in, I'm struggling to see what the 'compatibility issues' would be?
Don't get me wrong, the sound isn't dreadful or anything like that, with passives, just not up to the high standards I'm used to from top-notch active designs. You have to remember the benchmark I've got as an active preamp...
My modded Croft, in today's market, would likely retail for around £8-10k - it's a very capable, highly-optimised design, which allows serious insight into recordings, and a truly wide-open window onto the music, so that's what any passives are up against.
Interesting though, that LDRs, some of them despite not sounding anywhere near as good as the Croft, don't suffer from a lack of said 'drive', and consequently don't sound soft, so there must be something in their design that negates this.
They're powered by the mains supply, so perhaps that's part of it?
Marco.