For the S-video cable, look at (literally)
svideo.com. I use a whopping 75-feet run of their S-video and component cables, without an appreciable degradation of image quality. The price is very reasonable, too.
For audio interconnects, I've found that places such as
PartsExpress.com carry good cables (e.g. Acoustic Research) at better prices than my local RS, BB, CC, etc.
Incidentally, do they still include a set of in-the-box interconnects with a "hi-fi" gear such as the SACD/DVD-A player??? I doubt they do...