I am makeing a opne source EEG the programmable chip eeg.
I would like simoultaneous A/D readings more than 8-10 so know any SPI chips that would work. Also spark fun has some excelent USB chips to replace the one your using.
Also sparkfun.com USB chip has general purpouse IO that can control the spi digitaly vareable resistors on my Programmable chip EEG.
If you would like to look into it ...