If you have done much more riding than usual the soreness might be overuse rather than SPD related.
Probably this. When you apply being new to anything, and then doing a lot of it, it’s usually an adaption/overuse issue.
In the same position as yourself, as recently started using SPDs on a CX, and after doing a lot of reading I went with the foot further over the pedal…so the pedal spindle is slightly behind the ball of the foot, and just keep an eye on my feet when making a sharp turn 😉
How you getting on with the Pro6? I went with a steel framed Croix De Fer, but now contemplating swapping the frame out for the lighter Pro6, as I forgot just how many styles/fences I have to lift my bike over.