The URC-9800 version of the Producer 8 has an RF extender which the 15-1994 doesn't, and both the URC-9800 and URC-8800 versions have a much larger database of device codes. Also, they have the LCD screen which some people find useful.
But, learning is restircted to just the 6 special learning buttons, and you can't use those buttons for anything else, like macros or advanced codes. There aren't as many buttons on the Prod 8's as there are on the 15-1994 and generally I just don't like them!
But bear in mind that I'm a huge fan of the 15-1994 so I'm kinda biased!
Rob.
http://www.hifi-remote.com