Hi Dave,
I think the Ray is under-rated, it breathes better than the Dolphin and the scrubber is easier to pack. Downsides as you say the lungs are integrated with the jacket. It is also quite a small scrubber, I used a Ray scrubber in a homebuild and was getting breakthrough a lot sooner than I was expecting in cold water. They are well made bits of kit though, especially the DSV -- it would be better if it opened and closed a bit more smoothly but you can't have everything.
Definitely get some form of O2 monitor, I think diving an active SCR is dangerous without one. Active SCRs don't have any overt signs that there is a problem. You can still breathe them right up until you pass out if there is something wrong. A clogged orifice will still allow gas through but not at a rate to maintain the loop ppo2, you can overbreathe a properly functioning one, the IP of the reg may have drifted, etc. None of these give you any signs and having an ADV makes it worse because you may never notice any loss of loop volume.
On the Ray, I think the p-port on the bottom of the scrubber is where the Oxygauge is meant to plug in. Personally I'd say this was the worst possible place as you get a lot of moisture here, I wouldn't want a sensor there. On my Ray scrubber I drilled a hole in the lid, fitted a watertight cable gland and put the sensor in the top of the scrubber, cable through the gland and running to a handset. What might be easier for you is fitting a p-port into the counterlung and plugging it in there.
Once you start making mods to it though... next thing will be a KISS valve, some more sensors... soon you'll be on the darkside with a home made fully closed circuit Ray!!!
My geography isn't great so I'm not sure how far Geneva will be, but there is a dive shop in Neuchatel that I use when I dive in the Jura which sells Draeger bits and lime. Really nice shop and friendly staff. Also
www.danshop.com and
www.tecme.de, both in Germany, sell Draeger spares mail order.
I think why you don't get many postings on SCR is because I don't think they are all that useful (especially in the UK) apart from as you mention, a kind of taster RB to see if you can be bothered with them. With a 70min (I take that with a pinch of salt) life of the scrubber and a max depth of 20-odd metres, I'd reckon you could do the same diving safer and cheaper on a 12l bottle. I'm not a big fan of SCR though, I bought the guts of a Ray purely to convert to CCR.
Cheers,
Stuart