I am using 2 bluetooth dongles to get audio up to my Cardo Packtalk slim. I have everything under the seat. Been using the setup for about a year and it's been solid. The hardest part is finding bluetooth dongles that turn on and off with power. You need one receiver and one transmitter. There are tons of dongles that are battery powered and you have to push a button to get started every time you use them. These battery powered dongles will do you no good. Attaching a picture of the setup under my seat. I have a lot going on here. I have a dash cam, a buss power supply ect. I pulled the dongles and usb power up from the depths to be seen.

Pair the receiver to the Trophy Audio bluetooth. I am using Trophy Headset 1 paired to the receiver under the seat. I have a 1/8" audio plugged into the receiver dongle and run to the transmitter dongle. The transmitter dongle is paired to my Cardo.

This is the kind of dongle that will work. This one can be used for receiver or transmitter. I could only get this one to work as a receiver. I had to use a different transmitter.

This is a sample for what I used to power the dongles from my buss power.