Unlike my cover band members, I have been using IEMs for about 4 years playing for a large worship band. We have high quality IEM systems due to the fact that the venues (2500 plus seats) like to minimize stage volume so that they can better control the mix. Some of our amps are backstage or under trap doors in the floor. We all use IEMs. I started out with cheap Shure 215s. They work OK initially but you may soon reach their limits. Too many signals will cause distortion and you won't "feel" the bass as much as you would probably like. They also don't fit perfect. I moved on to Ultimate Ears Triple-Fi because they had an additional driver that allowed me to further separate bass from the higher frequency vocals and guitars. Eventually we all moved to custom molds from 1964 Audio (
1964 EARS In-Ear Monitor Design). I purchased the quad drivers which were designed specifically for bass players and drummers. I can not stress enough how much better these are than any universal IEMs. They block out ambient noise and allow me to control exactly what I want to hear. They have so much headroom, I could probably literally melt my brain before they start distorting. The bass is THICK if you want it to be. I only use my amp enough to create some vibrations to accompany the more-than-adeqate audio in my IEMs. These are just headphones by the way. They will plug into any wireless (or wired) IEM system that bands use. It is the headphones that come with the IEM systems that are low quality. This is what I'm trying to convey to my cover band guys. They can't get enough volume in certain frequencies without distortion. Just not going to happen with single-driver in-ear headpones. Vocalists can and do get away with lesser IEM headphones because they have the drums and bass frequencies much lower than their own etc., etc.
Anyway, I hope this helps. I just saw that 1964 Audio and other have some Black Friday deals going on. Good luck man. Rock on.
Brandon