The Handy's bluetooth communication protocol is complex. It uses protocom and protobuffers, which are difficult to integrate into Unreal Engine. Because of this, adding bluetooth support for the Handy is a lower priority. I'd recommend trying to toggle play/pause several times to see if the synchronization gets any better. HereSphere already tries to estimate the latency, but it assumes the latency is symmetric, meaning the uplink and downlink have the same latency, which might not always be the case.