Finally have some resolution. Not exactly what I wanted, but it will get the job done. This is specific to pre-2018 Goldwings.
I ended up with a Kennedy Electronics
95541 cellset connected to the GL1800 audio system. I got their radar detector cable for Escort 360 Max (you don't need attenuation - he custom made this cable for me about $50). You do need the single set to connect the radar detector through. Jonathon can set you up with what you need to do. I also got the cables to connect a 595 to the cell set.
To connect the Garmin XT, I got a
GPS connection from Cyclemax ($60). It feeds the GPS output ONLY to the intercom system. It has a volume adjustment and uses a 3.5mm input jack.
I got a
bluetooth device for the aux system from Electrical Connections ($35). I did not need the ground loop isolation for my bike. more common to need on 12-17 models. I had to solder a female 3 pole (stereo) jack in place of the aux connector (they used to have them with 3.5mm female jack - I don't l know if they still offer that or not.)
I connected Cyclemax unit both upstream of the 95441 and down stream. Made no difference. I could clearly hear the XT on the intercom system.
The 95441 allows you to choose where you have the sound play via a switch. I am set up with the 595 as the primary GPS because the sound is louder via the audio system (music, radio, CD system) and is in stereo. The XT only comes in on the intercom system and is not as loud and is in mono only. I don't know if that is due to the Electrical Connections unit being mono or the Cyclemax unit only supports mono.
The main thing is now I can hear the XT. I can use the master volume on it to turn down so I don't have them trying to talk over each other. But the XT allows me to clearly see it in bright sunlight where the 595 does not. I pair my phone with the 595 and can make phone calls using the 595 or dialing on the phone and both the passenger and I can hear and talk on the phone through the audio system. The Cyclemax unit is sound only and can be heard by both myself and the passenger.
The key is getting your speakers in the right location, as it really does affect sound quality and loudness. I had to move the ear pockets on both my and my wife's helmets to get them in the right place. The difference, volume levels at 8-12 on the intercom and10-12 on the main audio channel. Before I was pushing 15+ on the intercom and 20-25 on the audio. These are with
Earpeace filtered earplugs. I use the Music version with the max 24 db filters. They offer a moto version that goes to 26 db if you prefer. Very comfortable plugs. I am using the J&M 801 elite headset with the Aero IV boom mic and their speakers. It is still a wired system.
I was never able to get everything working with the SENA 50s units with either the Freewire or the SM10. The units are great, but just not quite there yet.
I am still testing and view this as an interim set up as I still want to end up with both XT in use and eliminate the 595. The bluetooth only interface on the XT is the weak link right now. Hopefully the bluetooth will get better and support talking to the XT for phone calls as well a stereo sound.