The reason why they don't work on the same pins is because SPI is an actual interface protocol. The reason the library uses those pins is because it can switch them faster as they are designed for the SPI interface. The TLC is not actually an SPI device. If it was communicating over SPI you would be able to use all the same pins with the exception of pin 10 which is the select pin which has to be unique to each device. This means that 1 device uses 4 pins, 2 devices use 5 pins, 3 use 6 pins. Look up SPI on wiki if you want to learn more.