What is the best exhaust to get to hear the turbo spool on mazdaspeed 6?

 

You'd be better off with a SRI if hearing the turbo spool is what you're after.

 

exactly... what Cam said..

you need to put on an Intake instead of an exhaust.

I personally have the CP-e intake and the ATP Turbo Inlet Pipe... you can hear the sweet sound of spool especially with light load light throttle input... mmm mmm mmm....