Just for fun, here is a set of 3 multiple TLC5940 examples.
The first is an ATmega168 w/ 2x TLC5940's running off 3 "AA" batteries (missing 6 LEDs due to no space).
The second is an ATmega168 driving a custom board with a pair of TLC5940's.
The last example has a board with an ATmega168 w/ 1x TLC5940 (w/ 1x LED) connected to another board w/ 2x TLC5940's.
I even did a lousy video (no audio, fan noise?) also http://youtu.be/DT54VHR94eo
you change NUM_TLCS in tlc_config.h... I spent several hours re-checking my wiring because I'd forgotten that I'd changed tlc_config.h on my laptop install, not my desktop. So when I ran BasicUse the LEDs on the 2nd TLC5940 would light at random.
You can tell if you've made a mistake with NUM_TLCS when not all the LEDs are lighting with BasicUse but the fade is still smooth with no "gaps" (times with no LEDs fading).
Double-check your wiring and you should be good to go. Then follow Demonic69's advice and try a tlc.setAll(4000) (followed by a tlc.update) to make sure you can light everything at once.