Disclaimer - My 3L is bone stock!
Now, from what I know about FI and how these things work, and from all the past experiences of modifying and blowing things up, you guys are being vague AF
Based on that signature, you have some supporting mods that should put you near the afore-mentioned 300hp output (crank).
I have no idea what that drivetrain loss is on the Touaregs, but I'd sure love to see a dyno chart of both a stock unit, and your modified one.
Initially, you say you want more PEAK HP output, but then later on in the same post, you say you want a broader torque curve..... this is a contradiction right there.....
VW engineered this "broad" torque curve given the limitations they had to work with.... (read EPA regulations). A turbo can only spool up so fast, based on various factors, including (but not limited to) airflow, inertia and rotational mass of components. It will be very difficult to gain all the extra HP you're after while trying to maintain the existing early torque & driveability, even if you're willing to throw out any emission compliance. The turbo is already sized on the small size, uses variable vanes, etc to provide the best of both worlds...... without getting into things like dual turbos, compound turbo setups, propane injection or increased displacement, you will not be able to gain much without giving up low end grunt.
I don't want to go into lecture mode here, but I'm hoping you know enough about what you're asking for and what I'm saying to get "my drift". There are some decent gains to be had by some fine tuning and small modifications which will definetly give you some extra grunt, but if you're taking about crazy gain expectations, you will have to spend crazy money and give up all sorts of driveability\reliability and simplicity to get there.