"With the ordinary artist, we can discover in his background and character where he drew his material from; with the genius, we often are unable to determine how he arrived at his startling conclusion. Armstrong's melodic gift was simply astonishing, and there is no explaining where it came from or how it worked its magic."
Except that Bix was no 'ordinary artist' that quote from Collier which you posted says it for me and sums up what I, personally, have always thought. We know where Bix got his extraordinary talent from - a very musical family. Where Louis got his is a complete mystery and that's what makes him a genius.