I've done mid-summer divisions of Miscanthus in my zone, although it's about the worst time of the year to do it. You have a bit shorter growing season, therefore less time for the divisions to establish roots before winter.

If you must do it, I'd wait to cut the foliage down until you actually do the divisions. Leave about a third of the foliage height, and take your divisions from the outer perimeter of the of the crowns only. Discard the rest of the plant.

A safer approach would be to wait until next spring, at haircut time, when the plant is just breaking dormancy. This gives the divisions most of their active growing season to establish new roots. I'd still limit the divisions to the perimeter, as it is the youngest and healthiest part of the crown.

Thanks Donn, I read some other threads on moving Miscanthus and there was mention of backhoes on clumps this size! I think I'll leave the grass and let the ladies tackle my daylilies instead. I wonder if a local nursery or other party might be interested in them next spring? Thanks for your help!