Years back, I came up with this setup when I removed the center muffler off of my GT3 and replaced it with a center bypass pipe. Studying the internal design a bell rang and I figured it could repurpose it on my '84 3.2. On a GT3, the system of this center muffler combined with the two side mufflers does a very good job of eliminating the drone, resonance, and loudness of the exhaust, until the valves open, after which it's basically an open exhaust. But without the two side mufflers, and just this center muffler, the noise suppression is only half of what it originally was. Resonance and drone on a 911 motor with headers is only an issue below 3000 rpm. Above that you can essentially have no mufflers and there's no drone. So in general what most people want to control and complain about with a loud exhaust is the noise below 3000 rpm. Since my car double dutied as a track and occasional street it was not a big deal to experiment with the setup.
You can reference the original thread here:
http://forums.pelicanparts.com/porsche-911-technical-forum/570968-quiet-muffler-doesnt-kill-power-does-one-exist.html
I used an MSD rpm switch set at 3000 rpm to vacuum actuate the Pierburg exhaust valves. I used the vacuum canister from a 944/964 with a check valve to collect and store the vacuum needed to actuate the valves through a Pierburg electronic solenoid. With the valves closed from idle to 3000 the exhaust sound is aggressive and deep but tolerable for me. It cuts the drone and resonance down by half vs an open exhaust or 2 in sport muffler. If you want a quiet exhaust or somewhat like stock, this is not the exhaust setup for you. When the valves are open above 3000 rpm, cruising on the highway, it is just about as quiet as a stock exhaust. But when you step on it full throttle, it wails and is almost as loud as an open exhaust header system you hear on a track car, which is to say it is awesome. I received lots of complements on the sound as the car came down the straights at the track at full throttle 6000+ rpm. Because you still leave a little gap into the muffler when the valves are open, it takes off some of the edge off the exhaust note. The combined tips at the center increases the pitch of the exhaust to a higher note closer to a GT3 vs a wider spaced exhaust setup. But the 3.2 note won't be confused with a GT3 as the motor doesn't have enough compression or rev out as high. For some heat i actually hose clamped a flexible exhaust pipe alongside one of the headers and was able to draw in some heat on a cold winter day.
On the dyno, on the 3.2 at around 250 hp, I tested it with and without the valves open and there was no power difference. On a GT3, at 400+hp, there is around a 20 hp difference.
This is the setup I run now on my GT3 too with a set of M&M headers, eliminating the side mufflers, as it's a lighter setup. Same difference, not as quiet as before, but tolerable, and at full throttle it's even louder outside the car.
The whole setup I think is overkill for a 3.2. On my 86 3.2, I just run the stock heat exchangers and muffler along but with a premuffler in place of the cat to reduce the heat above the at the heads and take off some weight.