I have the UltimaXL connected to a phone, Garmin 376C GPS, and two-way radio. Regarding the needed cables for the GPS, you will need to decide whether you will connect to the stock Garmin cable (with the bare wires on one end), or to the audio-out jack (which is either a 2.5 or 3.5mm jack - can't recall which). If connecting to the stock Garmin cable, go to your local electronics store for a female connector and connect it to the audio pair. Either way, the Baehr cables have full isolation and will be noise-free.
About connecting the Baehr power, I connected mine to an auxilliary fuse panel that is always hot. The Baehr powers down when the helmet cable is disconnected.