This route follows the obvious crack system up the inside of the Amphitheatre to the West bench. To begin, start near the inside western corner and locate the large crack system. (It starts just below the dihedral) Follow the line up through ledges and chimneys to the West bench. This would make a good beginner's lead as it is well protected for a flatirons route. Pat Ament rates this climb 4th class but I would disagree with this rating if you start in the crack and follow it the whole way. (Perhaps this is just an old-school rating)
Protection
Passive pro is sufficent for protecting the climb. Make the anchor in the alcove where the climb tops out. Long slings help (to thread boulders)
I think the route described here is in Rossiter's Flatirons guide (Falcon) as "Standard Inside East Face" (he calls it 4th Class). It would protect very well with lots of rests.
The Dihedral route is not 5.1, though probably not harder than 5.4 and offers good jams and stems directly up the dihedral formed with the junction of the first and second pinnacles.