On your question, simply split the signal at the DAC unbalanced outputs and run the other set of RCA cables to the EP500. Look forward to your impressions. But do you really need to add the EP500 if you are using the M80s for stereo duty? I would think you run a greater risk of introducing phase/crossover artifacts when collapsing the stereo bass information into the mono sub. About the only music that would benefit is deep organ.
Congrats on that new DAC. I'm in the process of adding a computer streaming front end into my stereo as well but going with a Benchmark DAC1 usb and a Slim Devices Duet for convenience so I can get my tunes wirelessly. The improved sound you are hearing is mainly attributable to the superior Dac and very low jitter compared to the Denon.
