Thank you! So I installed ASIO4ALL v2 with offline settings (as I can’t see a way of altering ASIO within Cubase), and used those to increase buffer size from 512 samples to 1024, and that solved the problem. I also tried increasing the latency, but that had no effect.
I’ll now read the threads about headphones, and see if I can work that out, and if not I’ll start my own thread.