yeah, as far as I know, the Ety ER-6 phones (as brian pointed out, the 6i phones don't work) are the only ones that you can use with the ety music plugs. I havn't seen any adaptors or evidence that the UE products are compatable with a stock set of plugs. If someone's got evidence to the contrary, I'd like to know.
On that matter, when you get plugs, try the ER-6 phones out really soon after, you'll know whether there are any defects in your plugs or not as the sound balance will be off from the norm (I found a defect in my left ear plug that way).