How can I use a turntable with a Krell Integrated?

You could buy a stand alone Phono Stage. The phono stage then plugs into one of the inputs on the integrated. It is simple but prices range all over. I use a Graham Slee SS for a high output moving coil cartridge which cost about $500. The type of cartridge will dictate what to get, but only to a limited extent. There is an extraordinary range of Phono stages as I have said some are indeed, much more expensive than your amplifier.

Ditto the above, would add that there are a few turntables with a built in phono pre-amp. They aren't usually in the league of stand alone units, but may serve as a start. Happy hunting.

The above assumes the Krell doesn't have an on board phono stage .......

They don't. At least the S 300i doesn't but it would be my clear choice.

I was looking at the Technics SL1200MK2. Not sure if it has a preamp or not. Thanks for the great info so far!