An update as I have been reworking my sounds lately - inspired by the addition of a Tube into the circuitry of modern keyboards like the KingKorg.
I decided that my keyboard sounds were lacking something. I have an old Korg N364 - a whole 8MB of sample data, and it pre-dates computer editors, and only a tiny screen and really complex on-board editing (lots of modes, menus, pages - much worse than an HD), so it is not easy to make edits to the sound and certainly not at sound check time. So I experimented with placing the FX Loop where the Keyboard sound comes into the HD500 in front of a Tube Comp and an Amp model.
Tube Comp is set Thresh=90 and no gain so that it just acts as a Limiter because keyboard that overdrives an amp when you don't want it too sounds bad.
The Amp is a Marshall P75 Pre with No Cab and the combination of this and the Tube Comp gives the keyboard that "valve warmth" and brightness, plus gives me knobs for tone control. It really made a difference to the sound
You can use a full Amp model if you want to copy John Lord, and there is no reason why the HD500 Rotary Model can't be used as well.