I just found a decent Audi and ordered two Phonak Naida IXs and an iCom. I want to do the same thing you are talking about doing. Basically an FM system or remote MIC that doesn’t cost $1000+ and works through the iCom.
Here is a solution I think might work. I will try it once I get my Naidas and recover from that financial outlay
I have worked with some microphone systems for "Electronic News Gathering (ENG), basically for field audio work. They make VHF and UHF wireless microphone systems that are completely battery powered and portable. They have better range then FM (over 100’, some 200’+) and they can be bought for relatively low cost.
I don’t think the iCom will accept a microphone level signal into its 1/8" jack, but many of the ENG receivers have a headphone output for monitoring the sound. I don’t see any reason that headphone level output couldn’t be plugged into the 1/8" jack on the iCom with an 1/8" male to male cable.
Here is one lower cost example of the microphone systems I am talking about. You will notice in the specs. it has “Headphone Monitoring”…
Here is a slightly higher end one…
You can also get some that support 2 remote Mics at once!
It will be a month or two before I can try this, but I think it will work. So if someone gets to it before I do, please let me know the results.