Thanks for all the tips, I'm making some progress. My soundcard is a Sound Blaster X-Fi (C8A0) which is ASIO, so aligning all the BIAB parameters for the card and MIDI out driver seems to have helped the latency issue. The keyboard at the top of the screen seems to be moving as fast as my fingers on the EWI now.

However now I've lost the sound output of the EWI through BIAB! The drums and backing tracks are audible, but now the EWI isn't. Two steps forward, one step back. The EWI sends just a MIDI signal not actual synthesized sounds, so I'm now trying to track this one down. It appears that somehow I've broken the connection between the EWI's MIDI signal and the software synth in the PC. It was Windows GSA before changing to the SBX-Fi ASIO driver. The EWI sends MIDI on channel 1, and I've made sure the SBX is set to channel 1.