Just bought the 245M along with some Powerbeats. An older Garmin headphone compatibility list said that Powerbeats were compatible. It would seem that a more recent list has changed that.
I definitely tried the standard pairing option and while I confirmed the Powerbeats pair just fine with my phone, the Garmin can't find them.
Edit: Solution found!!!
The answer wasn't on Garmin's side (sorry Garmin - my excuse is that there wasn't solid or consistent information on your end).
For those who are having problems pairing with Powerbeats or any other headphones, hopefully this works for you. I followed the directions provided by the headphone manufacturer to try to pair as if the device is Android. There were separate directions from normal pairing (figures since Powerbeats is now Apple) and MAGIC! They paired with full functionality.
Hope this helps someone.