Mysteries: HP5600 Wireless Printing Works on Airport Express, Not Extreme

I'd given up hope of being able to wireless print using my HP 5600 plugged into USB port of my Airport Extreme. I can see and connect to the printer, when I print, it goes into pause mode, and when I unpause, it shoots blank paper through the printer.

If I connect same printer via USB to my new Airport Express, it works like a champ.

Does this even make sense? I'd really like to use the Express in my living room for playing music, but I also want wireless printing.

Last ditch is trying the drivers shared from http://discussions.apple.com/message.jspa?messageID=10151042#10151042