I just installed the RS*R ExMag last night (replacing a GReddy EVO). First impression is that the exhaust is REALLY, REALLY quiet. As quiet as OEM at idle. With a load and medium throttle it is very relaxed and minimal exhaust note. With WOT it gets loud(ish) around 5k to 7k (when my VTEC crossover hits). Sounds very similar to the G35 coupe exhaust, a tad high pitch, but no rasp at all.
At interstate speeds (70-100) it is very quiet with low throttle input.
Compared to the EVO, it's a completely different animal. The EVO is deep and throaty. With my Zex camshaft, it would lope at idle similar to muscle cars (obviously not nearly as mean but reminiscent). The ExMag has no real notable exhaust note at idle.
I once heard an SP2 on a B16A2 and to compare the two... the SP2 is a bit louder than the ExMag. Of course, the B16A2 pushes a lot more air than the D16Z6, so maybe that's not a fair comparison.
Overall opinion: if you want high flow, low noise, and a nice looking tip, the ExMag fits the bill. If you want the cops to know you're coming so they can get their radar and laser ready, then you definitely don't want this exhaust -- they will never hear you coming.