I think I've found the perfect compromise
I thought I'd post up that reply for the benefit of others who might be in a similar situation. There were paragraphs, but copying and pasting to here seems to lose them.
People who go for a full in ceiling set up tend to be those that want everything to be as discreet as possible, and that is the main concern. The disadvantage with full in ceiling is that the coverage of those in ceiling speakers can be a little limited, especially in larger rooms. The front three are the most important, but it is those speakers that are usually furthest from the seating position. The wider dispersion of the KEF UniQ models helps, but you'll never usually be within the ideal dispersion of all of the speakers. This is why KEF brought out the motorised in ceiling speakers, so that they can be discreet, but when needed, they can be angled more towards the listening position.
If people go for part in ceiling/part in room installations, it is usually the front three being in room and the rears being in ceiling. There have been a few who have gone for in wall centre maybe, but fairly rare. The main issue you will have with using R Series as front left and right with an in ceiling centre is the difference in the point of their source. The front left and right are coming from more or less ear level, whereas the in ceiling would be coming from a point some two metres above that, which doesn't make for good sound panning across the front soundstage. I'd highly recommend keeping the front three as close to a single horizontal plane as possible. I have no problem with people going for in ceiling rear speakers, as these can be far more desirable than boxes, and can work well. To some extent, speakers behind us sound a bit different from those in front, no matter how close they are in design. Most "matching" rear speakers tend to sound different anyway, either because their cabinet volume is far smaller, the mid/bass drivers they use are smaller, efficiency is quite different, or because of their design (dipole/bipole etc). So don't worry if the rear speakers are a bit different - whatever you go for, they'll probably sound different anyway, and the only way around that is to go for exactly the same at the rear as you have at the front.
I would, at a total guess imagine that the driver area of the Ci380 is not too far off that of the Ci200, but with the Ci200 being an 8" driver, it will sound fuller with more presence, which is an advantage in a larger room, and will allow a lower crossover point - ideally we need to be looking between about 60-90Hz.
As for getting a suitable AV receiver, either something like the Yamaha RXA3030 or Anthem MRX710 are about as good as one box receivers get, and you're then into pre/power combinations. The above, particularly the Anthem, having good EQ systems, and the Anthem is particularly flexible, so whatever the system sounds like when it is installed, the Anthem should ensure you get the most out of the system.