Good pick up on that Mofimadness. Never thought to check on a phono stage on that preamp. In looking at it, though, it appears to be MM only (although it is probably an outstanding phono stage). This changes things considerably.
So in this case, just to complicate manners, presuming everything is working ok with the preamp and phono, Monako would just need to find a step up or head amp for the AT.
Alernatively, he could switch cartridges to a MM which might be a better proposition.
I'd probably go that route under the circumstances and put a few hundred into a MM cartridge to start off with and then upgrade perhaps if you feel vinyl is for you. No step-up or head amp to buy and no extra set of interconnects to worry about. I would definitely try to have the ML tested, especially the phono stage by hooking up to any phono with a MM cartridge to see if it is in good working order before doing anything if it's been in storage that long.
But that is a pretty impressive preamp if it is in good condition!!