As to using a PC to do all this, I've written curve-fitting programs
in the past, and the coding wouldn't be that hard. Adding an I/O box
to "press" the buttons on the EQ would be tedious, but not difficult.
The hardest part would be getting the RTA to output its data to the
parallel port constantly, not just when you press the "print" button.
The PC could handle all of the curve-fitting routines and calculate
the necessary adjustments, so you wouldn't have to reprogram the RTA
software except for the constant parallel port output feature.

I was thinking more along the lines of a winamp plugin. The RTA interfaace
wouldn't need to be parallel port either, and it wouldn't need to be
continuously upgraded either. Just when the "test"/"adjust" phase was
needed.