I like what you are saying about the ST-9000 being cleaner. At the show where I started messing with the setting the bass becomes distorted. This is from too much gain on the iRiver, no?
FYI I am going to a DJ/Electronic show so there is going to be lots of prolonged bass. I am thinking of using the DJ Set AGC setting and having the iRiver set to +10 then turn on the preamp gains and see where the levels are at. What do you guys think?
Distortion is probably from too much Iriver gain in combination with ST-9000 gain, yes. (Or from low voltage in the preamp, but less likely.)
You can easily notice this while taping: if the meters peak, clipping will occur. In Rockbox, set the screen to lighten up while clipping, you will be alerted and might adjust (or let Safety Clip do the adjustment for you).
For your next gig, I suggest setting the ST-9000 gain
before you start the recording on the rockbox. For loud gigs, start with +20 Church gain and +20 iriver gain, let Safety Clip adjust it down towards +-0. If you end up below 0dB on the Iriver, this means that +10dB on the ST-9000 would have been sufficient.