Marrakech - Foum Zguid routes?

[eightpot]

Just planning a Morocco trip for May (in Land Rovers) and looking at a couple of route options - appreciate any feedback or experience of the areas here:

I'll be using Marakesh as a jumping off point, then need to head towards Foum Zguid so I can follow the lake beds and erg Chegaga Eastwards, then follow the border around to Merzouga and back north.

Is there a good route over the Atlas from Marakesh other than on tarmac using the N9 towards Foum Zguid? I can see some tracks on google earth, but they could be potentially very slow and I don't want to take too long getting south.

Alternatively I had thought about going to the coast south of Agadir, doing an overnight camp on the shore, then heading East towards Tata - all the reports I read seem to suggest that between the coast and Tata is pretty bleak and just rocky harmada - anyhing worth seing here or is an Atlas route better?

thanks!