Stereo and be sure to use attenuators, as the board signal will likely overload the pre on that thing by a tremendous amount.
Not sure that the weaknesses of the mic preamps is in play when going Line In...
I'd try to get by without the attenuators...particularly if it is an RCA output...RCA > 1/4 should work just fine...
And more often than not - if you have to use an XLR output - there is a fader that can be adjusted somewhere...