I've dealt with the mono in-ear mix by using a mixer in my rack. I have my monitor mix from the board with no guitar into my line mixer, then add in stereo guitar. I don't know if you sing at all or not, but getting my vocals and guitar separated that way really helped me hear everything I needed to. Of course, that assumes you're able to get a personal monitor mix from the board. You can do something similar directly in the III, but it requires that you touch individual patches to set up, I like this for a global solution.
the extra mixer sounds like a cool idea, i think our whole band could benefit by getting more separation in our IEM mixes (ie. stereo spread for instruments, vocals/bass center) it'll help us out overall, but it's another investment to make i think down the line, we might upgrade things eventually, but our IEM rack (based around the xr18) was already a little investment
IMO it really depends what else is going on; the larger the band, the smaller the space in the stereo image the guitar can occupy. For the only guitar in a 3 piece I'd work in stereo to fill out the space, but as soon as there's another guitarist or keyboardist I'd think about going mono.
that's my current situation, i'm the only guitarist, but with mono IEMs, running mono atm, i'm also on the FM3 so stereo options are a tiny bit more limited to different cabs/stereo effects/enhancer, i'd love to try dual amps for example, which can open up more options , even having the same amp on both sides set slightly differently will make a difference i think
I run stereo to FOH, but we typically play small venues where someone sitting on the left side of the room can still hear what's coming out of the right-hand speaker, too. If necessary I can pan both channels to the middle. Also, the only time my left and right channels are different are when I'm using a stereo chorus or some type of ambient delay, which is only a few times per show. Stereo in those instances makes the guitar sound huge, IMO. Also, the wedge monitor in front of me is mono, so I make sure all of my presets translate well to mono.
are you running the same sort of cab/IR to both sides then or?
How do you run your mono setups? Do you just take the stereo spread of your time based effects and set them to zero? Or will you change out your stereo delays for mono delays? All other stereo effects just have a stereo spread I believe, no?
i've got a mono patch setup, ie. cab block summed/Center pan , mono delays (vintage digital being my favourite atm)
not running reverb, i've got a second delay setup in front of the amp actually for the few moments i have a cleanish tone going out (we play metal) it gives things more space/room but i don't have the cpu hit from the verb
if i was switching the patch to stereo on my fm3, i'd look at hard panning cabs/enhancer block maybe and then a stereo delay