Hello,
I used to have pass X1 preamp many years ago. It’s a very good unit, but I find it a bit on the warm/dark and lack a bit of detail. It was used with Krell amps as well. I am currently using krell 403E with krell evolution 707 processor/preamp. I think the Phantom preamp may share similar sound characteristic as the 707. I used Audioquest Sky balance interconnect then switched to cast. I find the cast has better details and dynamic.
So I would recommend the 402E with Phantom preamp using cast cables. I think this combination will get the most out of the krell units.
Rich