OK - I have half answered my own question.

I was not aware of the Move to function in Maxim DL. Once the guider is calibrated, I can click on a star, specify the location (in this case the X and Y position of my preferred position on the slit) and hit move and the guider will take the nominated star to that x, y position. I've managed to put a target star on the slit several times this evening using this technique.

I suspect that this explains why Bob was commenting on the move function only applying to the brightest star in the FOV. If the Auto option is selected, the guider will take the brightest star to the nominated position.

I suspect that Maxim does not permit both the source and target pixel positions to be fixed ie always take the star on the nominated central pixel to the target pixel. If it could, then this addresses the second item on my wish list.

I might take this up on with Diffraction to see if this can be done. If anyone is aware of how to do this, you will make me a very happy man by posting that here.