@bluorion I recommend you google a few basics on Class D amps. First of all, the D does not stand for digital; A, B, and C, were all already taken, so it was simply the next letter in the alphabet. A class D amplification circuit has a different topology/operation from the others.
Simplifying a lot, you'll find that many of the amps for sale contain three basic elements, an input buffer, the amp proper, and a power supply. There's a lot of mix and match with these three elements. There are different kinds of input buffer, and even ones that incorporate a tube. There are different amp modules, from Purifi, Hypex, IcePower and several others. There are switching-mode power supplies and linear power supplies; a subset of linear power supplies is those that employ toroidal transformers. Some makers allow you to "assemble" your own amp on their website selecting from the available alternatives.
From here it gets a lot more complicated. There are some genuine digital amps (not that many), and the next big thing will likely be GaN amplification. All of these terms are googleable.