My working band uses IEMs with our QSC Touchmix 16. I have suffered from tinnitus (since 2017) and need to either use IEMs or earplugs (with a more standard setup). Using a Sennheiser wireless, I use custom-fit 64-Audio IEMs A6t and monitor from the board. 64-Audio uses ports in the IEMs that Lance mentioned above. I love it because there are no weird air pressure issues even when playing in the hot sun during outdoor gigs, sweating like crazy, and they are comfortable with a capital C even for extensively long-wearing periods.
Once you get comfortable playing with in-ears, you will have a consistent nightly mix and can play with far more subtlety and nuance. It is different compared to playing with a speaker cab; in my situation, I have grown to be happy using them, and given my micro-managed hyper awareness about mix and tone to play inspired - it's an excellent way to perform.
In a P&W setting, which I also do (and have done so weekly since 2007), they are fantastic because I can get enough volume without any stage bleed from a cab - a guitar cab or a monitor.
In my working band, I run sound from the stage. Generally, the process is that we have a base mix for most rooms we play, but even if we play in a new space, we have a working base starting mix. I jump off stage for the first song or two (I use wireless for guitar and in-ears). I change by jumping back up, tweaking, jumping off, and checking it. It's efficient since we've been doing this almost weekly since 2016.
When first exploring IEMs - I had the luxury of checking out the non-custom testers of many top-end brands at the NAMM show, talking to the companies, and then making my choice and ordering a custom set. I got fit for them at a local audiologist doing a mold of my ear to 64-Audio's specs and sent them to them. If I recall, it took about six weeks; they came via FedEx. I started on the A3 from 64-Audio and then moved up to the A6 two years later (2019); they offered a great deal, and I jumped at it. I liked the people at the company; they answered all my questions, and I got a great vibe from them overall when I chose. I do not regret it one bit. With both sets of IEMs I have from them, there are zero issues, and I use these things multiple gigs almost weekly.