Diki, the 1/4-inch input is switchable between TRS line input and guitar input. If switched to guitar, then a Tonematch preset for acoustic guitar is working.
The mic input has a built-in mic preset also, plus e.q.
The RCA and 1/8-inch inputs, plus the guitar/line 1/4-inch input are all controlled by the same volume knob, so if you are using more than one set of inputs, you must control the volumes individually from their sources.
Or, do as I do and use a mixer.
Hammer, there was discussion earlier on the Bose forum about using just one extension and it was reported than it did no harm.
I tried it and it seemed to work fine.
I suppose there could be some sort of resistance factor built in though.
It will be interesting to see if they answer officially.
DonM