I and installing the raceline ypipe into my 2009-Nissan Maxima, and wanted to get opinions on which cat back exhaust system best would suit me, based on sound/performance. Also can I tie in the ypipe directly to the cat back system, or do I have to keep the midpipe/ 22" muffler/resinator in place?

 

Cat back systems will go from the Y-pipe to the rear of the car and includes the mid pipe.
Axle back systems will change after the mid pipe, or mostly just the mufflers and rear Y.

There is no best system, and preference is very subjective.

 

A aftermarket CB exhaust system sound is so subjective, like MaxDrvr said above.
Do some searching here for posted videos of other OP's that have these systems.
As far as performance don't expect much really. A Racingline Y-pipe along with a CB exhaust is the best way to get the most performance out of doing an exhaust upgrade mod...IMOP!

For the second part of your question.
Just my 2cents....I would safely jack your car up and climb under and get a good understanding of how the cars exhaust system is situated.