@flatcat:
Yes, this is the Roco Multimaus (with GB-transformer). You could make a digital start with it.
For this you need also in every loco a DCC decoder.
The 2nd booster could be good. But I don't know, I have a Gallus booster (but Gallus is not longer available).
Please ask the seller, if you could use it with the Roco Multimaus.