[NoDOHC]

Ok, you asked for it: Dynamic systems theory.

For air flow, the velocity is the flow variable (it is actually the flow rate, but for a constant diameter, we will call it velocity) the pressure is the effort variable.

Thus we will call the effort variable (pressure) voltage and the flow variable (velocity) current to make your electrical simulation work.

A muffler is not a strictly a dissipative element (which requires a pressure drop to cause a flow) It is much more complicated than that. The exhaust gas has an average flow (call it a DC component) and a time varying flow (call it an AC component). The actual waveform looks rather like a triangle wave. To the Average flow, the muffler can only cause back pressure, average flow is not the enemy, it is the friend, you do not want to touch the average flow at all. You can't hear the average flow anyway, it is the time varying fluctuations that you are attempting to attenuate.

The mufflers actually attenuate an alternating waveform (sum of several different frequency sinusoids). Most mufflers are tuned to certain frequencies and use destructive interference to cancel AC components of the exhaust waveform. The rotary has a harsh waveform due to the high blowdown and quick opening of the port. This gives a very quickly-rising waveform which must include many high frequency components. These components resonate near the natural frequency of the exhaust tubing (tap the exhaust pipe and listen to the note). The resonating exhaust will transmit the waveform to teh surrounding air under the car, notwithstanding the muffler. A piston engine is not an issue with this because they have slow-opening valves and therefore a much more sinusoidal exhaust pulse (lower components of high frequency).

I will not include any descriptions of this, take it at face value, or research Fourier transforms and series.

The earlier in the process the high frequency waveform is attenuated, the less air volume is excited by the exhaust pipe. this is why an early presilencer really helps quiet the rotary down.

Now to discuss as an electric circuit. The restriction in the exhaust (what causes the backpressure) is the dissipative element (the resistor), the attenuation of higher frequency is accomplished by accumulation chambers (the capacitors of the exhaust) and lower frequencies are attenuated by inertial chambers (the inductors of the exhaust)
Inertial chambers play the largest role in secondary scavenging of the engine.

A presilencer is a large chamber (capacitor), filled with steel wool (resistor). The resistor does not lie directly in line with the flow, but rather dissipates and sound that resonates outside the intended flow of the exhaust. This should make them a low-pass filter, except that the entire effect relies on the transfer of air through the sides of the pipe into the surrounding chamber. This is less likely to occur as the inertial forces of the air grow large relative to the viscous forces (which are the means by which the gas enters the holes). This ratio is called the Reynolds number (not that anyone cares). The Reynolds number increases with velocity, which means that at higher engine speeds, presilencers have little effect (due to the high average flow rate of the air). The good news is that a presilencer makes a small amount of back pressure at low revs, but very little at high revs.

From this description, I would conclude that two presilencers in parallel is better than two in series.

Now lets look at mufflers:
There are three types of muffler, the straight through (basically the same as a presilencer), the 'fart can' (multi chamber design, but straight-through construction), and the offset chambered muffler. (I am ignoring the old-school baffle/perforated pipe muffler, which simply restricts the flow until the exhaust is quiet at the great expense of backpressure). Straight through mufflers have been covered (presilencer).

The chambered muffler relies largely on acoustical wave-cancelling and is therefore very frequency specific. This is offset by selecting several or many different chamber sizes to maximize the attenuated frequencies. The wave-cancelling looks like an inductor in series and a capacitor to ground on the waveform. It resists changes in flow rate to drive a high pressure pulse which will then propagate back the pipe at a destructive phase angle. to the original sound. With several chambers, the sound can be attenuated very well. Please note that a properly-designed chambered muffler will make little to no backpressure and on a long exhaust system, they may actually decrease backpressure over a mufflerless system. Chambered mufflers rely on wave inertial energy to cancel each subsequent wave, this means that low flow rates (exhaust velocities) will hurt their attenuation performance. For this reason, it is much better to run two chambered mufflers in series than in parallel.

The 'fart can' is a special case of the chambered muffler. There is only a a single chamber and it is very small, meaning that it is tuned for a relatively high pulse frequency (engine speed). It also is incapable of attenuating the higher frequency (harsh) sounds at the higher speeds where the fundamental frequency is well attenuated. This accounts for the tinny, rattling noise that the 'fart can' makes at higher revs and the bigger-sounding-than-it-really-is throaty idle.

Basically for quiet exhaust, your single chambered muffler into dual straight through mufflers is probably your best bet to not completely sacrifice power on the altar of quiet.

I hope this helped.