I'm just working through the operations of the H4n and have a couple of questions:

- In 4 channel mode, is it possible to record the input from XLR 1 onto tracks 3 & 4 simultaneously?

- In 4 channel mode, can the levels of tracks 3 & 4 be adjusted independendly of each other?

From what I can see, I'm pretty sure that the answer to both these questions is no, but it would be great if I'm missing something.

why would you need a mono mic recorded onto two tracks? you can just pan track 3 to center in post... unless maybe you want one track at a lower gain for a safety track? hmmm... that would be a good idea!!!
in multitrack mode, input 1 can record to two tracks but will have only the one gain adjustment as it is only going through the one mic preamp... anyway, i think if safety is your purpose, the only option may be the on-board mics in 4 track mode at a lower gain, or using two externals, or both! you can 'unlink' input 1 and 2 and adjust the gain separately with the new firmware:

http://www.dvinfo.net/forum/all-things-audio/487699-h4n-firmware-update-enables.html

yes, that's exactly what I'd like to do - bracket record one mono input on tracks 3 and 4 at different levels for safety. I didn't know about the new firmware - thanks. That's something at least.