I get a lot of questions about running IEMs, so why not give you guys the tour?
First of all, from what I'm told, you either love them or hate them. I LOVE THEM, and here's why; I have been playing in loud bands for over 25 years and had just gotten accustomed to being nearly deaf by the end of a gig. We all know how cool it is to pass out after a hard night of gigging and wake up with your ears still ringing from the night before - that is ROCK AND ROLL BABY!! ha ha
Typically, I would hear my guitar just fine in the beginning of a gig, but as the night wore on, the cymbals would kill all my high-freq hearing. We all know how much of our guitar sound resides in precisely that range of freqs, so my usual gig routine included me 'gently' turning up my volume all night long.
Hearing fatigue is real. IEMs (can) eliminate this entirely. Of course, if you want, you can crank it up and defeat the whole purpose...but I digress
Our keyboard player invested in a really badass Presonus mixer for us all to run IEMs. The Presonus has a Wifi built into it, and we all connect to the mixer with iPods/iPhones using an app from Presonus (not available for the Droid - I had to purchase an iPod touch on craigslist). With the app, each band member can create their own headphone mix! I can have my vocals and my guitar louder than everything in my ears. Without the Presonus mixer, your soundman has to adjust your levels for you. But, once they're set, you're good to go virtually anywhere, any room size.
The keyboard player also purchased four 2-channel wireless mic packs for us to use. By using the left/right independently, we get 8 separate channels for headphones (there are only 6 of us, counting the sound man) The receivers for the wireless mic packs are all mounted in a rack under the mixer.
I also had to invest in a good set of noise canceling earphones, and they can get very expensive. If you get custom molded inserts, they can run you $300-$600, I opted for the generic 'earplug' style and got a set of Shure plugs for under $100. I use them inside my motorcycle helmet too - they rock.
One thing I hear from a lot of guitarists is that they simply must have their 4x12 cab behind them to 'feel' the music. This is utter BS. I played for a long time with two 4x12 cabs until I started putting a mic in front of ONE speaker for each gig. Why carry all those cabs if you're only hearing one speaker through the PA anyway?
I haven't owned a 4x12 in over 20 years. Now, I don't even bring an amp to gigs. My old stage monitor has been in the garage for almost two years now without any use at all = lots more floorspace onstage without monitors, BTW.
So, even without the Presonus, you could conceivably purchase a wireless mic pack, some good noise canceling earphones, and be using IEMs at your next gig. That is, if you mic your amp for gigs, which I have been doing for a very long time.
Your sound onstage is exactly what you hear when practicing at home, so NO surprises! I like that.