I am the author of the (now defunct) Frommer's Morocco guidebook, and I hope I can help.
I envisage two options for you:
- visit the Western High Atlas region (Asni, Imlil, Oukaimeden, Ouirgane) from Marrakech as a return day trip or overnight excursion, and visit the Moroccan Sahara (Erfoud, Merzouga, Erg Chebbi region) as a return two-night excursion from Fes. To travel between Marrakech and Fes, I would recommend the train or at the very least a bus, rather than a grand taxi (may include a change of taxis and potentially hazardous) or flying (exorbitantly expensive).
- do a one-way circuit from Marrakech to Fes via the Western High Atlas and Tizi n'Tichka pass to Ouarzazate, Dades and Todra gorges, Erfoud/Erg Chebbi, Midelt and Ifrane (have a look at a map of Morocco to visualize this itinerary).
Perhaps have a look at the following for more information:
Reputable and reliable tour companies include:
Marrakech-based Desert Majesty (Felicity Greenlaw-Weber); www.desertmajesty.com
Marrakech- and M'hamid- based Sheherezad Ventures (Rachel Blech); www.sheherazadventures.com
Fes-based Concierge Morocco (Helen Ranger); www.conciergemorocco.com
Fes-based Fes Art & Culture Travel (Hassan and Malika el Janah); www.festravel.ma
Marrakech-based Bouaouina Tours (Hassan Bouaouina); www.bouaouinatours.com
I'm sure you will now have more questions than answers, so feel free to post again.