An interesting part in the development of this variation was the Fischer vs Taimanov match, because I dont have acess to a good database this are the oldest games I know with this variation. (The are probably older games which I would like to see)
Taimanov's idea was to play Ng5-Ne6, sacing a pawn, it is rare that my MCO version gives that line as equal and is the one suggested, one would think improvements would have been found on all these years.
Right now Im taking a look at minor lines like 9.Bd2 and 9.Nd2 (Nd2 is way more common than Bd2 and perhaps better).
As usual Black should play f5, so he should unblock his f-pawn, there are different ways to do so and these ways lead to different games.
With 9...Nh5 you will usually have to take on f5 with the e7 knight as if you take with the pawn your knight on h5 will be hanging and tricks with Nxe5 will appear on the board.
With 9...Ne8 you can now take on f5 with a pawn but this choice is less active than Nh5 as from h5 your knight could, in some cases jump to f4.
Here is a diagram to illustrate your minds.