Yeah, I've got 5 3-drawer Can-Am thingies, and that cost me over $2000 7 years ago. Originally I kept everything in jewel cases, but after about 5 years I ran out of room in the Can-Ams, so I decided to put
some of my collection in Jewel Sleeves:
http://www.jewelsleeve.com/sleeves.html
They're clear vinyl with two pockets in the front to hold the CD and booklet (double CDs plus booklet fits just as easily), and a larger pocket on the back to hold the entire tray card. The pockets are lined with what looks like Bounce dryer sheets to prevent scratching.
I think I compressed 5 or 6 Can-Am drawers worth of jewel-cased CDs into about 2 1/3 drawers.
The Jewel Sleeves are about a half inch taller than a CD standing on end, so you can't stand the sleeves straight up in the Can-Am drawers--I have to leave some slack in each row of sleeves so they lie back and don't stand too tall to close the drawer (if that makes any sense).
The Jewel Sleeve company does make their own drawer units, so since you haven't already bought the Can-Am cases, you might want to go the whole Jewel Sleeve route. I'm satisfied with both the Can-Ams and the Jewel Sleeves, but neither system is cheap.
Plus you have to go through the psychological torment of actually getting rid of jewel cases (I would never have done it if I hadn't run out of space). Also, any CD that's in a Digipack or some other cardboard packaging can't be transferred into a sleeve unless you want to rip the cover apart. Minor drawbacks that only bother anal people like me.