I have both and the PK1 give you exactly that, deeper bass better clarity and I
think the mids on the PK2 are just to forward for me as well. Pk1 are a lot better with the mids
That's so smart of Yuin to design their two earbuds in a way so people would eventually upgrade anyway.
I think my advice to head-fiers is to go straight for PK1 and don't buy the PK2 then