just checked - for some reason you can control the mute, but not the solo - I guess the same as when recording to arrangement, where you couldn't record the solo-action.
hope thats just a bug they will fix.
one of the things i hated most about impulse was that i couldnt assign mute and solo to midi controls without stupid workarounds.
so Machinate, you are able to midi assign mute on the drum cells now, but not solo?