B6 s4 engine upgrades?

[Andy70]

I have an Audi s4 Avant v8 and can't help thinking that its under powered especially considering its a 4.2 but only putting out a similar power to an e46 m3 which is a highly tuned engine, so wondered if there were any mechanical upgrades I could to that would compliment a remap to improve the measly 15hp that engine tuners claim they can get from just a re-map alone? thanks!!

[Andy70]

exhaust surprises me actually, normally cars these days have pretty decent systems as standard I thought, but cool good advice, so a decent system would be just cat back or more? I always use 99 ron any way so all good there and a 40 quid K&N filter off ebay do? cheers for advice

[Andy70]

sorry, removing the cat, does not effect MOT and a tuning company told me once that sports cats or removing cat reduce torque, is that right?

[Andy70]

Cheers guys I'll bare that in mind