I would expect your question to be the other way around: What processors do video processing without having to do audio. Most good processors either have video conversion chips better than your BD/DVD player (Realta, Reon, etc) for improved picture quality and/or they have a bypass where the video signal is passed unaltered to your display with little if any degradation to the video quality.
However, the same cannot be said for the audio. Even fairly good processors (Integra/Onkyo Pro for example) have less-than-pristine analog audio sections that cannot be entirely bypassed when feeding audio signals to a good quality two channel preamp. There are situations where running balanced (or unbalanced) analog signals directly from a Marantz UD9004 or Denon A1UDCI BD/DVD player (for example) to a good balanced (or unbalanced) 2 channel preamp will result in improved sound quality. To do this, you have to add yet another pair of (expensive) interconnects from the BD/CDP to the 2 channel preamp. Interestingly, many current 2 channel preamps do have such a bypass for use in HT applications.
However, the same cannot be said for the audio. Even fairly good processors (Integra/Onkyo Pro for example) have less-than-pristine analog audio sections that cannot be entirely bypassed when feeding audio signals to a good quality two channel preamp. There are situations where running balanced (or unbalanced) analog signals directly from a Marantz UD9004 or Denon A1UDCI BD/DVD player (for example) to a good balanced (or unbalanced) 2 channel preamp will result in improved sound quality. To do this, you have to add yet another pair of (expensive) interconnects from the BD/CDP to the 2 channel preamp. Interestingly, many current 2 channel preamps do have such a bypass for use in HT applications.