Hi, i'm at the design stage of a similar display and came up with the same solution as you before i found this site.
My array is slightly smaller at 10x20 leds so i'll probably use the TLC5940's directly (needs 13 chips) and just multiplex the Red, Green and Blue lines of the array.
If i'd not bought the LEDS first (from Ebay) i'd have gone for common anode LEDs as they seem to be what all the controller chips are made for.

One thing i don't quite understand at the moment is why you (and others on the net) are pulsing the Blank pin every 4096 clocks.
As far as i can see from the data sheet it's only used to blank the display, it also resets the greyscale counter but won't that just wrap if you don't reset it ?

I'm using Pic micro on mine as that what i use at work.

Any updates on progress of your display ?

Jim