I don't see how you need a preamp with this unit. The mic input has *very* low noise.
Depending on sensitivity of the mic, I run between #2 and #6 approximately. For music I use low sens, for ambient I use high sens.
I did notice that higher ranges (above #6) don't seem to change the gain much.
Maybe Guysonic can do some measurements for us
. I found his work on the Edirol units very helpful.
Richard