Would an external DAC be of any benefit to me?

My primary source is a Western Digital HD TV media player, which is connected to my Onkyo TX-SR706 via HDMI. I have a McCormack DNA 0.5 deluxe connected to the AVR via pre-outs, which is then used to power my Usher BE-718's. With this particular setup the digital to analog conversion is being done by the Onkyo's onboard Cirrus Logic DAC. I'm also using the Onkyo's Audyssey EQ function (i.e. I'm using 'stereo' mode and not 'direct', as this yields an altogether more appealing sound).

I'd just like to know whether I could further improve the audio produced by my system if I added an external DAC between the media player and AVR.

Thanks!