How about something radical like a 8051-PIC interface?? :-)) Keep the 8051 as the master (of course) and PIC as the slave, and with I2C, you could use the PIC as little more than a "smart" USB peripheral... I assume if you use I2C, the inter-uC communication shouldn't be much of a problem.

Aint I full of wonderfully weird ideas? (I can hear the groans) :))

kundi