To recap, I was loaned a Resmed Airsense 10 by the lab for about 6 weeks back in Aug/Sep, and the results of that 'in home' test was that CPAP was not for me - too many 'treatment initiated centrals', so they called me in for an overnight sleep study. the first test was supposed to be a 'split' test (sleep + titration for an ASV) but I only got 2 hours sleep so had to come back for the titration, which is what happened last night.
In the lab, they had a Resmed device with 'IP21' and 'H5i' printed on the back (H5i is just the humidifier, I believe), and 'VPAP TX' on the top. The tech suggested this wasn't a 'consumer' machine, but a 'lab' machine - so not something I'm likely to be prescribed. Not sure what ResMed device is their standard consumer ASV machine.

Despite having my own pillow and duvet, I still could not get to sleep! Overall, from arrival at 8:15pm to departure at 5:30am, I got a whopping 2 hours of sleep! So it seems I'm just not cut out for sleep labs. The Tech said he got some good readings, though, and said the likely next step is I'll get a prescription from the Sleep Lab doctor.
I must say, after using the Resmed Airsense 10 for 6 weeks back in Sept, this device felt totally different (as it should, I guess, being an ASV rather than a CPAP) and it took some getting used to. This tech had me try yet another mask - this time, a Resmed Airtouch F20 with memory foam in place of the more usual silicone - seemed very comfortable.
Anyway - now I wait to hear from the sleep lab doc and find out what the next steps are.