Wow... not a lot of real science in here is there?
I suggest getting and reading the book
Scientific Design of Exhaust & Intake Systems by John C. Morrison, Philip Hubert Smith, Phillip H. Smith
It was written in the 1950s and 1960s. But the basics and the science is proven. It is the absolute basis for exhaust design. read that book, learn it, and then make good choices on exhaust design.
If the sound is too loud I would suggest adding some small flow through resonators ahead of the main muffler. You will need to do some playing with different sizes, but by adding a resonator you will change the note of the car without sacrificing performance.
One aspect you need to look at is how the Europeans do muffler systems. Before the world went green, most engine over 1600 had a pre-muffler about where the Cat sits in todays cars. Then they may have had one or two resonators after that before the main muffler. On rally setups they usually had one pre-muffler and then a main muffler. I bet that is all you need.
On the 1.9 liter I would actually use a 2.5" pipe for high RPM track usage, on the street I would use a 2.25 as that will be slightly quieter and provide the flow speed at low RPMs for good torque.
Keep bends to a minimum and please use mandrel bends