Bypassing boss br1180cd preamps, 1/4"?

[undrgrnd studio]

Do I have to use the line in RCA inputs to truly bypass the preamp?

I did a search and people have been saying to just plug the preamp into the 1/4" input and turn down the gain. However, this means I'm still passing through the cheap circuitry of the boss preamp and coloring the sound?

Is that correct?
Lets say I do use the 1/4" inputs for my preamps, which out of the 3 1/4" inputs am I supposed to use?

Why are there 3 1/4" inputs if there are only 2 recording channels?

 

[Dumby]

Inputs

There are two inputs the guitar/bass plus mic2 for the one input and mic1 in case you want to do simultaneous recording takes...Althought, I have found that the signal just doens't come out right. As for bypassing the preamps, I'm going to bypass my entire BR1180 for something else to record at home with.