What is 3 bytes?
If you are testing using a single DSC programmed for channel 1, there is really no reason to transmit all 4096 bytes in the universe. Sync + 3 data bytes + some padding. If the transmission is not repeating, you may want to pad the beginning with a couple of bytes. Sometimes the first byte or two have framing issues and no data is received.
Sync resets the channel number counter. When the first address is reached,the DSC or ssc will start collecting data until its buffer is full, then the dsc will use the values to set the timing for the PWM output that dims the LEDs or the ssc will start transmitting string data to the nodes. The dsc buffer should only be 3 bytes. The ssc buffer is 3 * #of nodes. Make sure the ssc start address + 3 * #of nodes does not exceed 4096 - if it does that string will always be a frame behind.