I can confirm monitoring 5+6 on DIN through headphones is fine, you just solo each channel. That's how I run most of the time.
Only use 7+8 DIN if I want to record more than 6 tracks.
Then I need a separate way to headphone monitor those two channels, via analog out of the v3.
I basically run everything in stereo mode all the time, and split the tracks later if need be.
DIN MON is for having the input levels of 7+8 display on the last two channels so you can set levels, not for routing audio to the headphone jack..
Hey dlh, that menu button - press and hold the front panel knob