Edwin Palmer Hoyt's Hitler's War contains this passage:
In January General von Arnim's army in Tunisia had enjoyed considerable success in limited actions against the Americans. The Germans had encountered the American 168th Infantry Regiment and had knocked it apart, capturing more than 600 prisoners. After interrogating the Americans in some depth to find out what sort of soldiers they were, the German intelligence officers came to the conclusion that they were pretty soft. The Americans were not politically indoctrinated, said their report. They did not know what they were fighting for except such things as "Mom's apple pie." They knew virtually nothing about the geography and politics of Europe. Most of them did not like their British allies. In a crisis their morale should disintegrate rapidly.
Field Marshal von Kesselring read this report with unusual interest. He had the overall responsibility for victory in Africa, and he knew how Hitler felt about the matter. Now he had not one but two Allied armies to combat. The best course was to take on one of them and whip it soundly. The best bet was the Americans.
On February 9, 1943, von Kesselring called together General von Arnim and Field Marshal Rommel. They met at the Luftwaffe base at Rennouch, Tunisia. The subject was the attack to be made on the Americans.
The senior intelligence officer of the Twenty-first Panzer Division made a report. Most important to von Kesselring was the fact that the GIs were badly led. Indeed, the French and British continued to refer to the Americans as "our Italians."
Hoyt doesn't say where he's sourcing these details from.
What were the primary sources for the 1943 capture of hundreds of soldiers from the 168th Infantry Regiment, and the German intelligence officers' reports on the Americans?
Did the two different reports mentioned survive and get collected somewhere? What are some more detailed secondary sources that cite the primary sources?