Just clearing up the project - closure.
New version: Adjusted thread priorities to give transmission priority. The stack sizes have been halved as well, to save IOP memory.
I've decided that I won't try to port the driver back to support existing homebrew software like OPL and SMS. I tried to, but ran into the old stability problems that I had last year... so I won't try doing that again.
Everyone else is welcome to try though. I've uploaded my work files :)
I've redirected downloads to a page on my web site to make things easier for me to maintain.