Charlie, so if I understand you correctly, you are using one of the existing tracks, in your example the Bass track, to store the APT that is a mix of all tracks (including Bass, right?

So, what happens to the Bass track while an APT is superimposed on top of it?

How do I solo just the Bass track?

Since the Bass track is frozen automatically, how do I regenerate the Bass track if I want to without erasing the APT?

How do I change the Bass track to a new RealTrack without erasing the APT?

Say I open an old project file where I have used your method, how do I even know what the Bass track is without erasing the APT?

The APT certainly seems interesting but so far it looks extremely counter-intuitive to hide an existing track and superimpose one over it. Seems like APTs should just be created in new tracks and not on top of existing ones.

And I cannot see this being faster as it requires many steps that a simple export does not.

But, the whole concept is interesting to me. Could I convert every track to be an APT of that track? And once I do that could I change key and retain the exact same riffs but in a different key? If so this is very interesting but still seems like a bit of a mess as the underlying tracks would still be frozen in the old key with the APTs changed to the new key.