hey Aaron,
Why dont you like Rugged Radios?
It looks like they do have interface cables see here
https://www.ruggedradios.com/index.php?main_page=product_info&cPath=53_48&products_id=90
https://www.ruggedradios.com/index.php?main_page=product_info&products_id=643
https://www.ruggedradios.com/index.php?main_page=product_info&cPath=53_256&products_id=603
So I spoke with a tech at RR and this was his response so it looks like it is possible
I can also use the RRP 3 which has input for 3 radio sources plus cell phone
https://www.ruggedradios.com/index.php?main_page=product_info&cPath=158_160&products_id=343
RRP102-A
RADIO 1 --> RRP102B
RADIO 1 --> CB Radio w/ CJ-CB Jumper
OUTPUT PIGTAIL --> Intercom system
RRP102-B
Radio 1 --> RM100
Radio 2 --> ICOM-IC-7100 (With possbly the CJ-ICOM-M jumper, you may need to custom build your cable using the CJ-MOBILE-UNI cable if the ICOM-M is not compatible, you would need the pinout from a handmic)
OUTPUT PIGTAIL --> RRP102A
Intercom pigtail would connect to RRP102A
You could use the RRP660PLUS intercom to connect wirelessly to your cell phone, or a hard connection via the CS-iPhone-6P on the [RRP660] (Non-Bluetooth)
The problem with all of this in the end is ensuring the microphone you are using would be compatible across the board. That being said, our dynamic microphones are compatible with the intercom itself, it would then be up to the radio to interpret the signal. I can assure you the RM100 will accept the signal from our dynamic microphone used in one of our headsets which is what I imagine you would be using.
Of course the 3 different radios would be using 3 different antennas, so I would not be able to consolidate there. This case is a bit of an oddity as far as requests go as we do not generally have someone running this many systems through one intercom but again, theoretically that is how it should work.The only two problems I could ever foresee would be the microphone compatibility between all sources and the added resistance setting up two switches inline like this. Let me know if this answers your questions and if I can assist you further.
The RRP100 can be used as well, my apologies, I meant to include that option and link along side the RRP102.