The torque converter automatic was the original type of automatic gearbox. Initially they had only 3 gears and were, in general, not great to drive. Currently they have at least 5 gears. BMW currently has an eight speed ZF sourced automatic box on offer. The torque converter is a hydraulic device which does the job of the clutch in a full manual car. They are good at damping all sorts of things which can be harmful to the whole drivetrain.
Your DSG is a far more modern approach to automatic transmission which dispenses with the hydraulics entirely. It is definitely progress, though the two autos I've owned (Nissan Primera (4 gears) and BMW 528i (6 gears)) both had a mechanism to lock the hydraulic torque converter under steady state operation. This helps fuel economy compared to the old fashioned autos of the 60s 70s and 80s. But the DSG approach, such as in your A5, is still superior in principle and will eventually replace the hydraulic boxes. The only downside is that they can be a little less smooth than the very finest torque converter devices.
You don't necessarily want a bigger turbo, you want one which can deliver more air than the standard one. A huge turbo is great if you want huge top end power but you will lose loads of flexibility in normal driving. Turbocharging is either a precise art or a vague science. Car makers are very good at finding a compromise. But this isn't to say that you can't improve upon things with careful product selection and professional advice. Plus a wallet that is getting heavy and needs a diet
