I've played in a power trio for about 18 months. During that time, I've invested in my own IEM system (Audio Technica M2 w/Westone UM-2's) primarily because we have a loud guitarist/BL (surprise, surprise) and the ear plugs I was using (Earasers) to keep my right ear from going deaf were making it hard for me to hear well enough to sing harmonies. Well, after a very busy summer, our drummer/soundman just said he's moving to in-ears because of persistent worsening of tinnitus in his right ear (any guess which side of the stage the guitar player is on?). Well, this apparently concerned our guitarist/BL greatly and he threatened to quit if the drummer started wearing them too. His primary concern is, if two of us on stage are wearing them, there is absolutely no way we, as a band, can ever be 'in the moment' and he'll be constantly fighting to engage/communicate with us. He refers to it as being 'under water' and not worth the hassle to continue playing. He said he's struggled to communicate with me since I started wearing them (news to me) because I always have my back to him in between songs (he likes to call songs at will versus following a predefined setlist...an issue for another day) and he doesn't want to yell at me. I told him that my set list is sitting on my amp, which is to my left (away from him) and I wasn't aware he was struggling. I use an ambient mic and told him I hear everything he's saying onstage and didn't realize he had an issue (as compromise, I told him I'd lay it on the ground to my right so I'd be facing him when I look at it). So my question for the masses is; is it possible to peacefully coexist in a band where some members are using IEMs and others are not? What challenges will arise or what do I need to be aware of to try and manage it before it becomes a problem. For the record, I took his threat seriously and began auditioning for other bands. I'm a firm believer in communication and if this was such a serious issue to threaten quitting over, then that tells me we are much more fragile than I believed and I need to find something a bit more stable.