Question about dac / sacd

I'm thinking about adding a DAC to my Sony 555es DVD, SACD, CD changer. Does the digital out on the Sony only output the cd signal, or would the SACD/DVD signal also benefit from the DAC?

CD only
The SACD signal would not, BUT if the disc were a hybrid, and most are, the DAC would take the CD layer of the SACD and work with that. That may or may not be an improvement upon the SACD playback of the 555es; it would depend entirely on the DAC and to some extent, I'd guess, upon the disc you were playing. It would also benefit the audio portion of your DVD play.

There is an outfit over in Switzerland that modifies Denon players so as to output multichannel digital signals that you can plug into outboard DACs and/or into devices like the Behringer DEQ2496 equalizer which accepts digital input. Apparently Switzerland does not have the laws which prohibit such a player over here.