Yes, the dried root is what you want to use. When we make our Echinacea tincture, we use the dried Angustifolia root from MR and "fresh" Purpurea root from PB, however the dried root from MR will work just as well.
Approximately twice a year PB will harvest and sell "fresh" Purpurea root from their own farm. To get the fresh root you have to let them know ahead of time how much you want. When they harvest, they will call you before they ship the root via UPS Second Day Air. It doesn't get much fresher than that.