Actually, I tested this communication process with MessagePack-CSharp where using the Typeless version of the serialization commands, the type is also passed direclty inside the message. So no need to send another message before that in this case.
After that, I just compare the type of the message with the list of types exported by my package.
If I switch to another solution, I will check TypeParsers more thoroughly.
As for Matrices, there is no support for complex numbers at the moment, which is a bit of a bummer for me but maybe somone will have an idea to support this via extension types, who knows…