A okay, make sense what you explained about the number of necessary soundchannels. I didn't had this in mind with the 2-player-simultan sound, which could cause a problem here then. All in all a good puzzle game that you wrote here and i am especially happy that we have a new good puzzle-game here now, cause this genre is one of my favourites.
A "Dr. Mario" version would also be great for the C64, maybe you can think about something like that, for one of your future projects? Best would be, WITH CPU-opponents like the SNES or Nintendo64 "Dr. Mario" versions have it.
Good puzzlers are always welcome and the C64 misses some of the big puzzle-classics. Also a "Puyo Puyo" version don't exist on the C64 until now. Fortunately "Bust a Move (Puzzle Bobble)" is in the pipeline and will come soon, but sadly without CPU-opponents as it seems, this is a little downgrade, because i often have no second human player available and only playing the puzzles in 1-player-mode could be a little bit boring in the long term. In the console-versions of "Bust a Move" i nearly only play the "VS Computer" modes and set the cpu-level to "hard". Then it makes the most fun.
Also in your "Space Orbs" choosable CPU-opponents would have been superb. The game is great, but then it would have been still better. Maybe in your next puzzler someting like this comes, it's definately a big plus to any puzzle-game when you can play against somebody even when no other human player is available. :)