dead cat????????

[rustyrex]

Hi all
 
Think my cats had it but not sure...any ideas??symptoms are
well low on boost 5 psi max on both turbos
high idle 1200-1500 (calms down occasionaly)
the odd little backfire or "pop"
exhaust note sounds different  
also sounds like i got a rattle snake somwere as i come off of light ish throttle???its not loud can only hear it with window open
 
cars a mostly standard jap import fd3
if i fit  a sports cat will i need a  new ecu,i  have a pan speed ecu at the moment:Hammer
 
cheers