Hi Chapeau, the GS10's you're looking at getting will be restricted in performance by the AV receiver you're currently using. If you got GS10's and used them with the CA640R you have, you'll get an improvement, and one I'm sure you'll be happy with, but the GS series deserve something more refined. With a better AV receiver, you'll get another jump in performance as it all works of course like a convoy does - held up by slowest vehicle (held back by lowest quality component).
Not sure if you plan to buy GS10's new, or go 2nd hand like the RS series, but if you go new, you'll be wanting to demo. If you arrange a demo, you could bring your AV receiver and compare against what your dealer has to offer and see if the difference is worth the outlay.
I'm guessing you may be looking 2nd hand though, so your options will be limited on electronics and will get less chance to try before you buy.
You're familiar with the MA sound with AVR280 and CA640R. Denon electronics will generally be a bit brighter, that is to say has a bit more treble and a bit sharper, some will like this extra edge, some will find it tiring. Rotel as I understand it is also more forward. NAD is more laid back. Yamaha tends to be more clinical and plenty of detail for movies, but I've never personally enjoyed the musicality myself, each to their own.
To summarise, you'll get the cosmetic benefit & WAF of the GS10's anyway, and some of the detail improvement whilst not losing a great deal of bass or bottom end. (GS10's apparently have very good quality and extension at the bass end of the spectrum, probably not a world away from the RS6's).
An upgrade to your AV electronics whether now or in the future can offer you quite a bit more from the GS10's. For now the CA will drive them, but don't be surprised if the sound quality jump isn't as large as you'd hoped when you switch them over.
I still think an AVR280 would make an ideal purchase, but the chances of getting one brand new are practically nil. The second hand market has a number for sale normally thoug.
If you're ever down this way again, let me know. You could always bring some kit down and we could swap some bits over and you can see the difference and if it's worth the outlay to partner with GS10's. I'm looking at buying a flat now, with viewings starting in a fortnight. Potentially by summer I'll have a flat wuith a reasonable size lounge so would be able to provide a more comfortable & better room than the demo I provided when you collected the RS series.