The Shelter 501 instructions recommends 100 ohms but of course you can switch and experiment with any ohm value with no possibility of system damage. I currently have my pre/phono section set at just under 1000 ohms with my 501 but it all depends on what your preferences are.
FYI, with this cartridge you will need at least 60db gain in the phono section which I think your Krell will handle.
Great cartridge...for me it's a keeper!!