Hi all, we are aware of this issue. As is standard practice, our mono earpiece is set up to sum the ring and tip to allow a stereo signal to be played as mono, as most professional IEM receivers are set up to output in either mono or stereo. It transpires that the whilst the Comtek PR-216 outputs a mono signal, it will output a stereo signal by playing the mono signal out of phase. This is where the issue emanates from - as our Sidekick Mono will sum a stereo signal, which in the case of the PR-216 will result in phase cancellation. A TRS to mono adaptor should sort this issue.