Short answer, you are fine to use both the console’s inputs and a digital stage box at the same time.
Long answer, the latency seen by using the inputs on the console is NOT the same as the latency you will see if you use a digital stage box. The stage box adds a slight amount of latency (but still stays under the .7ms total latency spec that A&H likes to use). However this difference is not large enough to be an issue unless you are trying to send the exact same signal through both a console’s input and a stage box input (ie your lead vocal through two different preamps – one on the console and one in the stage box). I cannot fathom a situation where someone would actually need/try to do this however.
