The Octasonic channels 7 and 8 have 35 dB LESS gain than channels 1-6. 7/8 are characterized as HOT channels, that is to say, they require a very hot signal to drive them.

If you install a mic and attempt to use it as a vocal mic (or other low level application) you will need to crank the input gain pot and you will probably encounter an unacceptable level of 60 Hz buzz.