I sometimes check the recording balance between sets on headphones. I use some cheapy Sony over the ear Walkman style headphones now. I want something that is easier to pack. I've seen the in ear buds that come with the iPod and thought those look like just the right thing for me. I've never heard what they sound like though.
Ah, if you're just checking between sets, then any old earbud 'phones will probably work, after all.
Brian, what ear phones do you use the ER6's? I actually do have some custom earplugs made by my audiologist. I have a pair that can be modded for In-ear monitoring if/when I want to spend the $$$.
I have the Etymotic ER-6. They fit right into my custom molded earplugs. The ER-6i, ER-4, Shure ExC, etc. won't fit. You may want to ask your audiologist if your plugs will accept the ER-6. Only hassle I can see going that route is you'd have to swap filters/'phones between sets. But if you have a second pair of plugs, then maybe you can forego that hassle.