I have a 1.8TS and i love it
There is actually quit a bit of a differences
The TS has forged internals (rods, pistons), intercoler on both sides, a slightly bigger exhaust housing (allowing for more exhaust flow at higher rpms and capable of making more hp, up to 230hp and 368Nm (240Nm original) with BSR chip and with little modification up to 300), better turbo impeller and compressor wheel, bigger injectors and a tune making those extra 27hp. The rest of the drive train is different too, higher final drive 4.38:1 vs 37:1), closer and higher ratio gear box, lighter flywheel and a griper clutch. Suspension wise it have bigger anti roll bars (32mm front, 18mm back), lower and stiffer springs and matching shocks, bigger brakes, 321mm front and 256 in the back. Suspension and drive train is basically from an B5 S4. In the interior it was standard with sport seats and the Bose system.
The engine is, as said above, capable of making around 300 with easy mods. I have heard of people putting an s3 (not sure witch generation) map, injectors and downpipe/cat on and chip tune it as an s3... With a couple extra easy mods and a real tune it can probably near 350 on the tire. A race cat (or test pipe), better charge pipes and elbows, different re-circulation valve and maybe some meth would go a long way (probably head studs/bolts and gasket to). Tho clutch, flywheel and brake upgrades would be recommend at that level. And of course an exhaust is recommended from the beginning
I have a Milltech cat back that has an amazing daily sound level
And as some one else said, intake do not make more hps but it will make turbo sounds louder