You seem to be in a very tricky situation.
Rx2 - 1x8 inch bass/mid driver and 1inch tweeter
Rx6 - 1 x6 inch bass 1x6 inch bass/mid and 1 inch tweeter
Common sense would say for a a stereo setup get yourself a FS instead of the BS + Sub option .
There are pros and cons for both
Although MA are fairly easy to driver.
A FS will always require more amp power. Infact more the power better.
With a BS you can get away with a medium rated integrated. Also if you factor that if you add a subwoofer into the equation, you are reducng the load on the BS speaker from producing difficult low freq and in turn it will play a lot cleaner.
However integrating a sub into a stereo setup is not that easy. it may take you days or even weeks to get it right. However the final outcome will be better than the equivalent FS.
There are are some pretty high end stereo setups that use Subs. A example that comes to mind is Bhagwan our FM uses 2 martin Logan Depth subs with his Tidal BS and Cadence Monoblocks
I even know someone who has the B&W 805D with 2 JLAudio Subs mated to Classe amps
Blasto as you know I have the lB&W 685 + RythmikAudio Servo F15HP sub. I can safely say it sounds way better than the 684. (not compared it to the 683 so cant comment)
I have the Arcam Preamp preouts connected to the inputs of the Sub and the Sub line outs to the Rotel monoblocks.
The Rotels get a signal of 80hz and above . So in turn play a lot cleaner and the BS gets 80hz and above . So overall I have taken a lot of load off the PA's as well as the speakers
Yes the sub + BS costs probably twice as much as the 684 and probably even costlier than the 683.
But I cant even fathom the sort of amp I would require to drive the FS from the same stable. That in itself would negate the cost advantage
With MA however you don't need this sort of power.
I have never heard the Sunfire Sub. but it should be pretty good.
If you can look at some other subs as well REL / Rythmik Audio
or DIY a brilliant sub using Gr-research drivers and A370 plate amp.
At the end of the day its a tough choice and its only you that can take the final call.
- F l a s h -