Yeah the sport would have been my first option for sure, worth even the risk of it not being loud enough. I got a deal on a good looking race version and I had to jump all over it.
I agree with your logic, stock exhaust and castles DP's. You would think that makes sense. I already know the problem lies in the fact there are no cats. That is the secret ingredient keeping that cheap sounding bark out of the system. I know for certain that installing some cheap cats in front of the Eisenmann would do it some crazy justice. They would literally serve the function of secondary cats like most AMG's have. The problem of course is that you'd be restricting airflow and that's no good either.
Here's my e63 with mid length headers, catless, to stock muffler:
Here's the same car with Kleemann high flow cats (200 cpsi).
It's almost the same sound. The high flow cats did nothing for the noise and I ended up going back to stock exhaust with the mid length headers.
Point is it's all a pipe dream. The only thing that will get rid of the bark is a good 600+ cpsi cat. That's when you get into quality sound territory.
Here's the X with stock DP's and Eisenmann Race: