Memphis and Minneapolis are about 700 miles apart by road. Split the difference and you arrive near Kansas City, the city closest to the halfway point between them. That puts roughly 7 hr 45 min of driving on the Memphis side and 8 hr 38 min on the Minneapolis side — the fairest single meeting point among the cities near the middle.
That's a half-day drive from each side, so Kansas City suits an overnight or a weekend rather than a quick coffee — long enough to want a reason to stay, short enough to drive.
If Kansas City doesn't have what you're after, Omaha and Chicago are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Memphis and Minneapolis.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.