"Unfortunately" the schiit and other competitors are not distributed (and if so in limited quantity) in Germany. So, only sabaj, smsl, topping, loxjie.L30 measures quite well as all the other toppings for their latest iterations. If 1990 is what you are sticking with and you have no desire to upgrade - sure L30 is still good.
If you live in the states you can get one of Schiit offerings as well for cheap, check the reviews here - magni is probably what you will be looking for.
If you want to upgrade to something different - you will need to be a bit more specific.
What is the fuss about the serial numbers and what is affecting regarding topping? Also. what about the volume dials and controls and stepping of db?
Thank you!