1. The shach himself is maikel. He asking a stira in the rem"a 2. The shach clearly is asking from the rem"a by iruy mkli chalav lkli basar 3. As for an answer to the stira see pm"g which would limit the original question to a kli chalav and not a parve kli.
IIRC that us only when it is both keilim at the same time
It seems like I understood the shach different than the 2 if you. Guess I gotta go learn it again, but from what I recall:
2. I agree he is asking from iruy but he doesn't learn like the taz in sif 3 that iruy makes it like the case of yorah choleves, hence he's disagreement with the rema, the reason he holds the rem"a assurs in that case it's bc it's Nat, bar Nat lisur.
3. The shach himself answers the stirah, that in sif 2 the rem"a wasnot taking about iruy,
As for what the shach himself holds, I recall that he is macmer like the mharshal. But we are discussing the rem"a