Yeah, I would just need to go from the Atmel, running at 3.3V, sending CHK and MOSI to the LED driver which runs at 5V. The logic voltage on the driver is, at its minimum, 0.8 x VCC, and at its max, VCC. So that means for a "high" to be registered, it has to be between 4V and 5V. (A "low" is registered between 0V and 1V.)
So I would need to go from low to high for those two signals. There's nothing coming back TO the Atmel.