I love my H4n too. I use 4CH mode often for live recordings. I take vocal only and instruments only sub-group outs to feed the line inputs and align with the mic tracks in Reaper or StudioOne.
It is an extra step to separate the stereo track to two-mono. Maybe this could be changed in a future firmware update? It's easy to split them in Sound Forge.
I'll test the 1/8" line input when I have a chance next week.
Clip of mixed 4CH recording of live band:
http://www.scredco.com/mp3/band_clip.wav (client wanted the vocals up, gtrs were too loud in the room, thus not in the live mix. that's why room mics are up a bit. )
and another from an opera benefit:
http://www.scredco.com/mp3/zoom_opera.mp3
Zoom H4n, mics only, on a little tripod, on a table, in a booth down the pub @20ft from band w/small vocal PA. Don't think I did anything but convert to mp3. 80Hz HPF and Concert limiter engaged as I recall.
http://www.scredco.com/mp3/zoom_mics.mp3
These are recordings I give away. I don't agonise over the mixes. A quick once over and out they go...
Oh, here's a location recording of 4JULY fireworks. (mics only) good sub action.
http://www.scredco.com/mp3/FW.wav
This thing is so much fun!