Bose Free Soundsport Wireless works great. Just be sure watch is on right wrist because the main earplug is on right side. Or at times, you can just use the left earplug and put the right earplug in your running belt if you have one and watch can be on either side and use your right ear for sensing surrounding.
My jaybird x2s are working with my new 645M with no dropouts (left wrist). Audio controls on the headphones also work as expected.
Edit: went for my first real run (had been walking before) with 645M and x2 today, and my experience was... not good. The connection is spotty to say the least. The odd part is that it's unacceptably bad for a while, then fine for a while, then worse again. I prefer this watch to my (returned) Apple Watch S3 in almost every way, but if I cannot fix this issue, it's going back. This was just not an acceptable experience for a watch sold as a music player. Will try my wife's X3s tomorrow, which are on Garmin's verified list.
As mentioned before my Jaybird Run (true wireless headphones) work absolutely fine , even a few metres away from the watch (separated by a wall) . So i assume there can be NO "general" connection issue caused by the watch's hardware. ;-)
My Jaybird Run earbuds do not work properly. If I put my arm down the music skips. If I raise it to "running height" it is OK. But when I start moving it starts skipping and won't stop. Will try my beats by dre wireless 2 next time. Otherwise I return the watch and buy the non-music version.
Ok, the wife's Jaybird X3s don't do any better than my X2s. To say I'm disappointed is an understatement. This watch does so many things so well, but this is going to be a dealbreaker if I can't get it working correctly. Already have the X2 and AirPods, so I'd rather not get a third BT headset, but I guess I'd consider it if it would save this watch for me...
Just an addition to my previous post on Beats X earbuds. Have gone jogging with them on the last two days and absolutely no drop outs or issues experienced. I wear the watch on my left wrist. Very pleased with how well the music played and from my experience of walking/jogging they seem to be a good fit for the watch for left wrist wearers. I've not tried the watch on my right wrist.
Ran this morning (outdoors) with Bose SoundSport Wireless Headphones. Very disappointed that music cut out regularly when wearing on Left Wrist. Works fine on Right Wrist. Garmin says compatible with Bose SoundSport and that it works "Good with watch on either wrist." Garmin's support website suggests wearing in such a way that the Bluetooth receiver is not snug against your head to improve reception and that reception is far better indoors. So Garmin's solution is for me to run indoors or hold my right earbud (with the Bluetooth receiver in it) away from my head/ear.
Just back from a 21 mile run and used Plantronics Backbeat Fit. Garmin advise that the watch is better on the right wrist but as I always where my watches on the left I tried it that way. When running slowly got lent of dropouts but when moving faster none at all. I’ll have to try switching to the right wrist next time out, bit of a pain that
