Is it using a cable throttle or DBW? If it's using cable then it's probably using the M3.8.x ECU, which is a pretty simple and "dumb" ECU, doesn't even use a wideband sensor.
The bad news is that less and less people want to touch that ECU as it usually requires physically soldering a new chip onto it (although you can flash some 3.8.x by feeding power to the correct pin in the OBD port, but not all of them). I live in Poland and couldn't find a single tuner within 150km radius that would want to tune it.
If you want to tune it yourself you can look for a P&P "standalone" ECU, I'm using one right now from RM racing electronics and while it's not a perfect ECU and lacks some features, it's certainly possible to tune it well enough so that it's enjoyable to drive (takes some time if you're new to tuning though)
That being said, AGU is a pretty durable 1.8T, it has the forged crank and some solid pistons, however just like other 1.8T - the rods are the weak point, so you have to be pretty conservative with the torque. I had it in my Octavia and I have it right now in my A3. Stock engine w/ a k03s and a downpipe makes ~210-220hp (didn't dyno it yet, but feels similar if not a bit faster than my previous 1.8T in an Octavia that dyno'd 210hp / 380nm, I lowered the peak torque a bit after the dyno)
Stock AGU with the right tune can probably get close to 200, but the k03 is what's limiting its performance, especially on a stock TIP and DP.