If you run your IEM unit in mono (as I do) it won't be an issue.
If you are coming straight out of a headphone amp in stereo with no wireless IEM then you may need a stereo to mono connector.
A rolls pm351 box is switchable from stereo to mono and would be ideal if you are not using a wireless IEM that can be switched between mono and stereo.
I hope this helps. Also, check out 1964ears.com for your ear bud, they are a very good company to with with.
Gear: Eden WT800B, 610xlt, 210xst (2) Sunn1200s, Berg NV412 Basses: Musicman SR5 & SR4, Fender CS 64 Jazz, CS Reggie Hamilton V, MIJ '89 P bass, MIJ '94 Jazz Fretless.