I do not have a BMW GPS on my bike. Using instructions I found on the K1600 forum, I successfully paired my Sena 50R to the bike and the Garmin XT and then paired the Garmin XT to my Andriod phone as follows:

1. On bike, delete all BT pairings 

2. On bike, shut down audio system

3. Delete all pairings on Garmin XT and shut XT off

4. Delete all sena pairings on phone (if exist) and shut BT off

5. Pair Sena with helmet 1 on bike (I'm not sure which Sena BT configuration gets used here?)

6. Power up Garmin XT and pair Sena to GPS using the "GPS connect option" on the Sena

7. Pair phone (in my case Android) with Garmin XT GPS

I can make calls by using the "Hey Google call John Doe on Mobile" but I cannot hear any responses from the "Hey Google" process. When the phone hears the command to call, the phone places the call and I see the "Call in progress" on the Garmin XT GPS. 

I can control the volume of the call conversation using the bike's wonder wheel. 

I cannot communicate using "Hey Google" after the call completes and I want to hang up the phone so the phone basicaly times out when the person I'm speaking to hangs up the phone. 

I cannot use the "Hey Sena" commands to control the phone because the phone is not paired with the Sena directly. The phone is only paired to the Garmin XT GPS for phone calls which also allows me to play music from my phone.

I don't understand the Sena configuration controls to choose the pairing options: (Phone 1, Phone 2, GPS, and a couple more I can't remember right now). 

So my question is:

In order to use the "Hey Sena" voice commands to the phone, is it possible add another pairing to connect the phone directly to the Sena 50R while maintaining the Bluetooth connections to the bike and the Garmin XT?

If this is possible, I need to know how to pair the Sena 50R to the phone in terms of which configuration I should use in the Sena's Bluetooth options.