i just did a quick search on google for "high flow cat scion xb" and came up with this page:

http://www.prostreetonline.com/parts/scion/xb/
(they mention having high flow cats for xb's a little further on down the page)

i would suggest giving them a call, i couldnt find high flow cats listed on magnaflows website... the other thing you should ask about is a cat that automatically gives you 2 exit pipes from 1 entrance, and viola- even more piping down the line (and no need for a ypipe!) then you would need 2 resonators, but youd still get a much louder deep sound without getting too raspy.

-jon

 

oh man... i plead the fifth....