I've cracked it! I looked in lsmod - and I have to blow my own trumpet and way it was before I read your input, pmpatrick, thank you for that - and saw no mention of sata at all, although the pata module was listed. Thinking I'd little to lose apart from my own sanity, I then added 'sata_nv' to modprobe.preload in the hope of forcing it. I rebooted and eureka - there was the optical device in PCC>Hardware and PCC>Local disks. I checked lsmod once again and now the module is entered there. And it plays DVD's. Thank you OP for telling me what to look for. But I'm still interested as to why that module wasn't in lsmod. It should have been, surely? And as it wasn't, is there, could there be something rocky about this install?
But thank you, guys for your help.