My current player has 4 DACs, 2 mono DACs for every channel. I presumed that the Denon in question uses similar strategy.
Channel separation is an obvious benefit of having separate DACs for every channel. By using 2 or more DACs per channel the following could be achieved (one DAC gets the original signal, another DAC gets signal that was inverted in the digital domain):
1) any noise from internal circuitry or RF picked up on the way to the output is cancelled out when the difference of two signals is computed (assuming that what influenced one channel, influenced the other one similarly. it's an alright assumption, because even if noise is not cancelled out completely, it gets significantly reduced),
2) assuming DACs are the same (which they probably are) and their SNR (or relative error) is some epsilon, after the signals from DACs (V and -V each with absolute error of at most |epsilon * V|) go through differential amp, the result has twice the intensity of the original signal (2 * V) but the absolute error is only sqrt((epsilon * V) ^ 2 + (epsilon * (-V)) ^ 2) = sqrt(2) * epsilon * V, thus the relative error of the final signal is sqrt(2) * epsilon * V / (2 * V) = 1 / sqrt(2) * epsilon, or 3db smaller than output of each DAC by itself.
Bridging 4 DACs probably goes as follows:
(DAC (V) - DAC (-V)) - (DAC (-V) - DAC (V))
[- stands for diff. amp, DAC (V) -- DAC that processed the original signal, DAC (-V) -- DAC that processes the digitally inverted signal].
As I said, I don't know if Denon does exactly that, but this mechanism is used sometimes for the reasons I outlined...