Not sure what you mean. If you have the Nad connected via USB, then if you want audio output, then two choices
1) Digital out, so the NAD is acting as a switch, and outputs whatever the NAD is receiving, it just bypasses from in to out
b) Analogue out, the NAD is acting like a DAC, output is fixed at 100% (line level) via RCA
c) Analogue out, the NAD is acting like a DAC, output is variable (pre-out) via RCA
What do you want to output the signal from the NAD into? And for what reason? So you want the Audiolab MDAC to act as a DAC, and Denon just to be "hub" for your gear?
NAD is lacking on digital out and analogue out, so I think you're up the creek.
If I think what you want to do, you'll need item like this. Digital out
https://hometheaterhifi.com/volume_10_2/images/lexicon-mc-12b-back-large-4-2003.jpg
SPDIF output that is between the RS232 ports and IEC
or L/R zone 2/record outputs