@rosettif What "mono check" is? You mean about the problem (I found this annoying too) when only one SID is uses and you hear from only left/right then? With headphones it's quite unpleasant experience. It can be addressed somehow, just hmm the problem here, that if you introduce something "against" it, it will have different behaviour than on the real M65 :-O Maybe that problem should be solved there, and an emulator just needs to follow what it wants to emulate then :)
Having a separated C65 emulator btw is cool. First of all there is no "C65" as a single standard. That machine is never released or finished. Even at hardware level there are differences. A C65 (only) emulator should emulate an "average" C65 or better, most of the versions really exists, with allowing to choose. And yes, "preservation" of the development platform (ie: C65) is a nice thing to do. At the other hand, and M65 emulator (or M65 hardware itself too) it's "just" want M65 is decided to implement as "C65" in its own sense. For example M65 fixed the RMW behaviour for better compatibility in C64 mode, but it's not the case of a real C65. And so on (the plan to have "CPU personalties" maybe bound to I/O mode is like this, it can greatly improve the C64 mode compatibility but again, it's something never existed on a real C65). Also, trying to emulate C65 is also cool, that it's more simple than the M65, so it's easier to even try new things out at emulator level/emulation techniques which is anyway "close enough" what M65 may want too.
What I see more or less to be true: as C65 is not a "single" platform, and not even easily accessible (it would costs a lot to buy a C65, but there is not so much good C65 emulators either out there, afaik mame/mess can emulate it, I've never tried, but only several years ago) so what M65 does here may create the "C65 standard" in some form what never existed for real before because of the lack of finished development of C65 by Commodore. It's another question that it even extends it, creating a second new "standard" ie the M65.
I really like C64DTV, by the way. I really miss the continuity of that platform. I've had chat with Jeri Ellsworth once, and she stated that the major problem not having enough time to really do what she wanted over the basic design principle that it should run the games what it was shipped with. All the new features she pushed in was essentially an "optional" feature, and I think it's only her attitude to even put in, as nothing would use it in its default entity it was sold for (ie run games it was shipped with, all the other stuffs of usage meant to be "hacking" by the user than the "normal" purpose already). This is more or less true for some critical point of C64 compatibility as well. If it could run the desired on-the-flash software it was OK (even if it means to modify the games when it was more easy, I guess). Anyway, what she told me, that she would really like to release it as a more "computer form" factor, with finished features (ie overscan mode, some compatibility/timing differences with real C64, etc etc) and more number + more easy "hacking". Just she doesn't own for real the Verilog sources, as it was a contract stuff to make it. Or something this I had the idea about after reading her messages (I can be wrong to interpret all of these after a short chat, so please do not take my word that she really meant all of this!). But, what I wanted to say, C64DTV for one aspect had more easy task: it's basically a C64 + enhanced stuff. And C64 is a quite well defined notion how it should work on deep hardware levels. It's somewhat more complicated in case of C65, so M65 too, where M65 is basically a C65 + enhanced stuff originally.
Again, these are only my personal thoughts and feelings, as always.
Oh, and what I wanted to write with DTV as a major point: M65 at least open source, while DTV is not so much ...