well epoxy primers are usually nice and hard and water proof, 2k are soft and sand-able. I don't really see how a non sand-able primer and a sand-able primer can be combined. It would be interesting to play with some.
FWIW, The term 2K only refers to the fact that the paint requires a catalyst (activator) to cure, it has nothing to do with the purpose of the paint. I have never seen an automotive "epoxy" paint that was not a 2K system.