kudos to dubbedown, some tremendously useful info in this thread for 3.0si owners.
the euro headers are already catless and are oem quality, so i wouldn't bother swapping them out. if u're concerned about emissions, then race cats in section 1 and a revised section 2 are really the only other alternatives. mufflers add hardly any power and are just means to vastly changing exhaust sound, whether for better or worse. tune is really the only way to go for noticeable and appreciable gains in addition to swapping ur final drive.