why not use the Arduino PWM? It has six channels
I'm not just using 1 chip. I need to control 17 RGB strips with full PWM. I'm planning my initial breadboarding to use a arduino mega to drive it, I suspect I might be pushing it's limit with it though, and I want it to do more than just talk to the lights (it will be talking to an ethernet chip and an SD card as well).
There is also very little space to hide cables, so running 68 cables around will look very ugly.
What I want to do is have a small sub-board for each strip (or 2), with just a 4 wire link to all of them, that way I can use a piece of CAT5 to make it look neat. This requires 3 or 6 PWM channels on each sub-board, 16 is overkill and racks up the price quite a bit (particularly if I scale up the numbers later)