I revised my inline mixer changes and created a pull request for it ( https://github.com/Uzebox/uzebox/pull/88 ). I wish to merge it in, if you can, please test with your games, particularly whether the noise channel didn't change (it shouldn't).
The next thing I will most likely attempt is to work on the VSync mixer to trim down its memory requirements. This would be useful for Mode 72, leaving even more RAM to work with.
EDIT: I verified that the noise channel works properly, so I merged the new inline mixer in. Larry: It may be useful to recompile Iros with it as it gives some extra CPU time for the game (occasionally it still seems to be missing a frame).