You can not support a Northeast African origin for contemporary Negro-Egyptian speakers. A complete literature review of the history of the climatic conditions in the Sahara and Northeast Africa over the past 20ky indicates that the Negro-Egyptian speakers originated in the Sahara.. You have not fully understood N. Drake’s work on the geography of Africa. As a result, you have failed to recognize that there were varying periods of “arid Sahara” and “Green Sahara”.
As I have outlined elsewhere there were two different African populations before the origination of Negro-Egyptian speakers: the Khoisan and the Pgymies. The Khoisan expanded out of Africa 40+kya, while the Pgymies probably began to exit Africa 22kya.
The Negro-Egyptian speakers probably originated in the Chad Basin near the MegaChad Lake. During the Holocene a giant lake, known as Lake Mega-Chad (LMC), extended over more than 350,000 km2 in southern Sahara.
Lake Chad is the remnant of a former inland sea, palaeolake Mega-Chad. At its largest, sometime before 5,000 BC, Lake Mega-Chad was the largest of four Saharan palaeolakes and is estimated to have covered an area of 400,000 km2 (150,000 sq mi), larger than the Caspian Sea is today. It was near these sites that the Aqualithic and Ounanian cultures existed.
The Chad Basin covers an area of approximately 2,434,000 square kilometers, equivalent to 8% of the total area of the African continent. The Chad Basin is surrounded by high mountain ranges which rise up to the highland of the North Equatorial Plateau. The Negro-Egyptian speakers lived in the plains and mountains around the Lake.
During the LGM there were many settlements in the Chad Basin and Highland regions of the Sahara.
On the plains they founded the Maa civilization. The Maa civilization may have originated in the the Bodélé Depression. The Bodélé is the deepest part of the basin. It was around 155 meters above sea level.
Between 4,410 and 5,280 BP, the lake MegaChad started to contract The oldest archaeological sites found after the desiccation of Lake Megachad date to about 4,000 BP. This corresponds to the migration of Maa people into Upper Egypt, as illustrated by the rise of Amma/Ammon worshipers in Egypt. It was the refugees from Maa who founded the Egyptian 18 Dynasty.
While Saharan Africa was well watered during the rise of the Aqualithic and Ounanian cultures was well watered Northeast Africa was not.
Ethiopean Plateau was arid between 17,000-10,000 years ago. This is why we see the rise of the Aqualithic and Ounanian cultures---the homelands of the Negro-Egyptian speakers in the Sahara--- not Northeast Africa.
A good site discussing the climate and geography during the LGM in Africa is located at: http://www.esd.ornl.gov/projects/qen/new_africa.html