To connect 2 GLD’s you need an extension card like DANTE! Unless you don’t have an extension slot at a Qu-16, there’s actually no possibility to connect a Qu-16 and a GLD-80 together!
I recommend a DANTE-Card for the GLD if you want to do multitrack recording, or only use the Qu-16 for FoH Mix AND Multitrack-Recording!
Another (cheap) way to do a multitrack recording without loosing the GLD-80 for FoH would be to use a analog splitter! However.. for playback you would need to repatch the splitter to have the signal now comming from the Qu-16 Multitrack into the GLD!