According to the manual - both the xlr and rca inputs are active at the same time regardless of the setting of the analog input switch.
So you should be fine going xlr in. I have heard though, that using the xlr as a line input essentially attenuates the signal so as to not overload the mic pre. Apparantly, the rca line in does not do this - I have always been told that it is better to use the rca - but I do not really know for sure...