2 DACs: 1 best for movies, 1 best for audio, why?

I have a home theater system integrated into my 2-channel system. pre/pro connects to pre-amp using home theater bypass input on pre-amp. I have a dedicated 2-channel DAC and transport. I have a BRP/DVD going into the pre/pro as well as FIOS TV. Then, here comes the dilemma: I have an AppleTV that I use as both a music server, and sometimes for video. The AppleTV has an optical out. I can send that output to either the pre/pro or to the 2-Channel DAC. What's strange is that the AppleTV sounds better on video when I send it to the pre-pro, but it sounds better on music when I send it to the 2-channel DAC. Movies (voices, sound effects) don't sound as real through the 2-channel DAC. Similarly, music doesn't sound as real through the pre/pro. Any thoughts? Note that this is not a 5.1 verus 2.1 issue: I am comparing 2 channel video to channel audio.
Maybe the music is 16 bit,and the video is 24 bit.One DAC might get along with one better(16bit),while the other might get along with the 24bit better? Just guessing.
that's very interesting, and quite possible. Thanks!