Heh.. another converted! Nice write up! The reason I have 2 993's is that I could not give up the cabrio. Indeed with the top down the sound, smells and the whole experience is out of this world and better than a coupe...
As for the exhaust there are many alternatives to the expensive Porsche system. I guess if you have it when you buy the car is a good thing, but there are certainly other alternatives to make any 911 sound amazing. Yes there is a RUF system which is identical to the one you describe with the bypass valve, but its expensive too... My preferes solution is to mount a set of Supercups on and then fire up the engine... The grin you are going to experience will most certainly be very very difficult to get rid off!