I use the Hearback system and am very pleased with it. I usually set mine up like this:
Channel 1/2: Stereo Pair used for playback of some arbitrary basic set of tracks.
Channel 3-7: Individual instruments/vocals that the performer may want to tweak.
Channel 8: Reverb (or Delay) return for the performer to adjust the amount reverb they want to help them deliver the best performance. Most singers seem to really like having control of this.
Normally after just a couple of minutes of instruction the performer can take total charge of their own mix. There have been a few non-techy types that have need a little help.
Each remote has two headphone outputs and I have not had any problems getting enough volume out of them. I haven't had a need to record a drummer who needed an extremely loud headphone mix but these get quite loud. I even get sufficient level with the older AKG 240m 600ohm headphones.
The cat-5 connections make things very easy to setup and get the remotes where you need them.
Just a quick note regarding the reverb feed to the headphones. I run direct monitoring for most of the tracks being recorded but the reverb is coming from Sonar plugins. This lets me virtually forget about latency. Any latency on the reverb is just a little pre-delay for the reverb signal. It doesn't cause any problems even at relatively high latencies as long as the main monitoring is direct.
I certainly wouldn't want to go back to having to create a bunch of mixes for everyone with headphones during a session. Much easier to let them do their own and after a few minutes most people don't have any problems getting them set just the way they want them. I see a lot of people tweaking them even during their performance. That would be very difficult if the AE is setting up all of the mixes.
Don