Dewdman42,
Thanks for posting that. Although the CPU % looks high, the total load in the graph window is still low. On my Steinway, I maxxed-out th polyphony, but I'm only using a stereo set and no reverb plugin. See attachment.
Something I did notice and I'd suggest is to turn off your Wi-Fi and use ethernet if possible. Same with Bluetooth. Disable any attached webcam. The Synchron stuff is great, but it's a CPU hog. You're not doing anything wrong. Try a simpler patch like the stereo "recording" Decca Tree and disable a couple of the room mic channels.
Limit all DSP inside of the Synchron Player like reverb: Use a "master reverb" that works with the whole mix and it should gel fine. If you have an external reverb unit, use that just for monitoring and only use the fancy convolution ones for when your printing final FX tracks and aren't concerned with latency, etc. YMMV.
I hope this helps or gives you a better idea. Cheers!