Ah, but what I meant was to completely combine them so that it's a dedicated full-duplex object.
If you did that, it wouldn't matter whether it plays ok with the separate wave/play object, cause what that object does would already be combined and super-optmized in a single object, dedicated to the task of multitrack-recording.
The way you offer the mux objects in various sizes, I think that's the way to do it. As long as the smallest version can at least record two mono tracks while simultaneously playing-back four mono tracks, it would be fair to say you have a dedicated full-duplex object for multi-track recording and playback.
So for example, the smallest full-duplex SD card object would have two ins and four outs all in one object:
If it works ok, and you can get even more tracks, then just add another two tracks to each object:
Might even make it up to 16 track out and perhaps 4 or 8 ins depending on how well the optimization goes. Anyway, I'm clueless as to the technicalities/abilities, it's up to King Axoloti and his workmates
But yup, would love to see super-optimized/integrated objects dedicated to multi-track recorder tasks.