Time to fess up. It was all me. Stupid, stupid me. Classic, removed 2 lines of code whose function I didn't understand as they sort of seemed to not do much. Idiot.
Anyway, now I've slapped myself about the head with a large plank, let me point out that the latency problem has now gone. Absolutely, utterly, totally gone. There is to a first approximation NO LATENCY*. None. You can throw fingers all over the keyboard and sounds just come out. At the same time as you press the key. Wicked. Crisp and immediate and fantastic.
This thing is a beast. Video to follow, but most likely not til Tuesday folks, I think I need to take the Bank Holiday weekend off.
*Yes, proper signal processing folks and physicists can shoot me for that, but you all know what I mean.