I was very much in your same shoes and I did a lot of research before I bought my AR catted DP. I didn't want the car to sound louder and prefer it to be stock quiet (I had the BMW PE before and sold it because it was too loud and droned).
So to answer your question, it's safe to say there's no way to get the performance of an aftermarket DP, without an increase in the sound level.
Here are some thoughts:
1. More likely than not, you will hear wastegate rattle (especially at cold starts, you might even get a few glances at your car from other people), this is the sound that bothers me the most
2. Your exhaust sounds will be louder even with a catted DP (if you're really sensitive to sounds, you will definitely notice), but it's fairly tame
3. Any problem you experience with the turbos will be blamed at your DP by the dealership (since turbos are covered to 8 years/82,000 miles)
4. More likely than not, you will smell unburnt fuel at stops
5. SES light may appear
1. More HP
2. Less turbo lag
3. More HP potential with tunes
I'm really happy with my AR catted DP, except for point 1, 4, and 5 in my cons list. Hopefully, I can get rid of these issues with my next upgrade and fix.