Paul,
I just tried your code and saw much better results over what I had. Thanks!
(At first I thought I had a column out, till I realized I only have a 2 color matrix!)
I think the concept of a duty cycle and not toggling shutdown any old time made the difference.
I need to understand what you're doing a little better, and then try the technique in my ap.
I notice you didn't use the LedControl lib. Do you see any reason why it couldn't be used?
Hope the 3rd color works out. Then I'll be off to the store to get another MAX and a new matrix!