Here is a link to the manual. http://www.tech21nyc.com/support/man...Driver-OM2.pdf
Basically the switch that corresponds to the 1/4 output has settings for instrument level which is best when going to a bass amp and line level which is better for using directly to a power amp or a mixers line input.
The switches that correspond to the XLR are for using phantom power or lifting the ground to eliminate ground hum. The other switch provides a -20dB pad (instrument level) and line level.