Far as I can tell, most outputs are post-EQ and the aux is switchable pre or post, so plug the mic into the channel input of your choice and you should be good to go whether you're coming out of the direct outs or buss outs or an aux switched to POST.
If your mic is bright, first of all, try to solve the problem with better mic placement or choose a mic that works better for your purpose. I think of using channel EQs on the way in as a last resort because it doesn't actually solve your problem which is that the mic isn't picking up the source like you want it to. If you absolutely must EQ on the way into the recorder and your problem is the mic is too bright, I don't understand why you'd want to solve this by adding low-mids. If it's too bright, roll off the highs a little, don't muck with the low mids unless there's a problem in the low mids. If your guitars are missing some low-mid, try to solve this by either EQ'ing the guitar amp itself, placing the mic a little closer to the speaker cone and/or more towards the outside of the speaker cone where there will be more going on in the lows. I think you can solve your problem with mic placement alone rather than recorder channel EQ.