Eight. I used all but the highest two bands, because I wanted to have the option open of using your bass/treble adjustments for broader "overall tone" controls.

Something I forgot to mention about this whole process:

I get very little response out of my system above frequencies in the teens (13000 and above). Not sure if this is a limitation of the microphone, a limitaiton of my sound card's available sampling rates, or if my amps and speakers just don't do a good job of the highest frequencies. So I didn't really try to do any corrections up there, and it made it easier for me to leave those last two bands alone.