Hello gentlemen...I'm back from a long absence...(Thank God I have DSL again!)
At any rate...here is my opinion on the exhausts. I have heard them in person, so I'm not speculating. The Supersprint has a nice clear, low, non-throaty sound at idea...much like stock. However at higher RPMs...it sounds clean and far from ricey.
The Stromung is a tad bit deeper in sounds through the RPM range. Unlike the Supersprint, the Stormung is more forgiving with regards to HP gains, and doesn't completely depend on a perfectly tuned engine for any gain. For best performance, this is my choice.
If sound is what you're looking for...the B&B Tri-Flow is by far the best I've ever heard. It doesn't quite have the low rumble of a v-8...but it sound extremely aggressive at all RPMs. For sound and show, this is my choice.
So...in my opinion...here's the ranking:
1. B&B Tri-Flow
2. Stromung
3. SuperSprint
Cost-wise (List Price)...here's how they stack up for the 325i:
B&B Triflow: $850
Stromung: $665
SuperSprint: $607-660
I currently sell 2 of the 3 well below list and I'm working on getting the Tri-Flow. I'll be happy to help with any other info you need
I've also recently added Remus to the list...but have not yet heard it in person. I'll most likely hear it early next month when I head down to LA for some meetings with Remus-USA.
BTW - With an exhaust...performance is nice...but realistically...don't expect more than 10-15hp at best gain from an exhaust...regardless of who makes it.