I live in So Cal and recently bought an 02 CC. I listened to the GHL straight pipes on a car in the Orange County dealership showroom. It sounded good but when I called GHL, it was just a direct fit replacement made of 2 1/2" polished stainless steel welded together. I liked the straight cut style and staggered but seemed like it was expensive at $1500+labor. I was told that it pops on the down shift.
I cut my rear mufflers off (and had them temporarily dump straight down) and drove it a few days to see if I liked the sound. It sounded great, very throaty but because it had limited backpressure, the acceleration was a little flat. That also happened on a Porsche I had where I used direct pipes to bypass the cat. The car also had resonance like you would expect at less than 3000 RPM. It popped on deceleration and blipped too strongly when downshifting. I then had the exhaust system designed to use 1 3/4" pipes to get back the needed backpressure without using resonators since the distance was very short and I didn't want to also lose too much of the sound. I used four 2 1/2" stainless steel tips but was warned that they will heat up, want to move from the heat, and change color. I took care of that by inserting a sleeve inside the 2 1/2" SS with insulation material to isolate the heat. I had to have the pipes mounted with brackets firmly since they still go through where the original pipes were between the bumpers. It looks good and sounds great. I think having it custom built is the only way to go and it was a lot cheaper than a Tubi ($3k) with the same sound and without the low end resonance with a Tubi (below 3k RPM).
In case anyone in SoCal is interested in building their own, I used Valencia Muffler in Fullerton 714 879 7439. Ask for Joe, he's been welding for 40 years and does a great professional job. Cost was under $1000 and took 2 days. He told me he did some work on cars for the "Fast and Furious" movie.