Either use the Ultra’s line out into the Denon’s Audio in sockets using a double RCA cable, or choose the Ultra’s coax out into the Denon’s Digital Audio In CBL/SAT coaxial using a standard coax cable, or use the Ultra’s optical out into the Denon’s digital audio in TV Audio or Media Player optical inputs using the supplied optical cable.
In the first case, you’ll be using the Ultra’s DAC, while in the other cases, you’ll be using the AVR’s DAC - use whichever sounds best to you