Not sure if any of my suggestions will help you (but I did breed cats for 20 years & have a few ideas that might help) ... so here goes ...
First, make sure your cat(s) are on the best possible diet. The better the food, the more it gets digested. The reason dogs like cat litter, is the smell of food after digestion. Unfortunately, this won't cure the problem entirely but more digested / less food smell in the litterbox.
Second, the obvious ... trying to remove all waste from the box as quicly as possible. Have you seen the "Littermaid" boxes that auto-clean themselves? Less in the box ... less to be fascinated with. Check them out here:
http://www.littermaid.com/
Third, an enclosure for the cat box ... here's a good product that looks good too
http://www.hidytidy.com/ or a less expensive version here:
http://www.petsmart.com/global/produ...N=2047564&Ne=2
And, lastly, this type of litter box might work well for you too:
http://www.petsmart.com/global/produ...N=2047564&Ne=2
P.S. My dog has the same fixation on the litterpan but I've blocked his access & so far, that's working.
Kitty Litter 
