There is no merge functionality implemented within ENTTEC's Pixel Controllers. This means that if you send two different sources on the same Universe, the output will flicker. 

ENTTEC recommend the use of sACN on different priorities to be able to perform a seamless changeover between control sources on your network.

Each port (Universe/Source) can be set at a priority level between 1 and 200 (200 being the highest, 100 being the default). If there are two or more sources of sACN on a network, both sending the identical universe number, the universe with the highest sACN priority will be used by the DMX node to output. If one of the sACN sources goes offline, the source with the next highest priority will be used.

The sources will merge on an HTP (highest-takes-precedence) basis if they both have the same priority.

All ENTTEC sACN products work on a per-universe priority – not per channel.