Tony, thanks for your reply. I think that the transistors are there to switch on the halos via logic outputs from the decoder, and that the pcb is wired for ESU decoders such as yours or the Loksound V4. A Zimo 644D will only drive the halos if the transistors are bypassed as described by John Gymer of YouChoos. Not sure I want to go this route; your experience is pointing me to ESU!
Anyone from Dapol care to comment!