So why not go with the PS Audio BHK amps? You’ll have synergy between the BHK pre and amps and eliminate the guess work
Otherwise the Pass X250.8 would be my choice. It should match as far as output impedance of BHK pre to input impedance of the X250.8 but PS Audio doesn’t list gain. Pass preamps have around 9db gain. If the PS Audio is much higher you will have limited usable volume range. Which may or may not be a problem. All this is a guess work I’m talking about eliminating.
In any case, I would suggest emailing PS Audio with Pass and Krell specs to confirm compatibility.