Most High-Flow cats will pass emissions.
I would not do a straight pipe and no muffler (sound,resonance, loss of bottom-end power).
Some can do 1 muffler and work very well and others might be too loud. Depends on the pipe Diameter, Muffler construction and so on.
It's best to HEAR before buying and if possible to get a ride or drive someone elses car that's already done.
I have a '98.5 Audi 1.8t. My twin Borla 2.5" diam Techtonics System was great before the high-flow cat and downpipe... but afterward it got a lot louder!