To use the MP3 Probe in Direct Wired Mode, Renishaw recommends the MI5, MI8 or MI8-4.
I bought an MI8 on a make offer eBay Posting for $50. It has arrived and appears in as-new condition. My MP3 was listed at $499, I made an offer of $249.50 and it was accepted almost instantly. It came with a K&T Adapter that is as big as the Tormach spindle!
gary