For digital cables (DVI, digital audio etc..) cable quality is far less important - just get the signal there uninterupted. As far as analog cables, shielding, resistance, the quality and fit of the connections (tight and thick). There are a ton of other things and to be honest the best place to research or asking is not xbox-scene. Head to the forums at www.avsforum.com or www.hometheaterspot.com. Keep in mind this is the holy war of topics. Some people feel that they can tell minute differences in even the highest quality cabling (like $8500 interconnects - i.e. Transparent Opus). Also, the quality of the rest of your setup will play a very large part since connecting a perfect cable to an average system will not give you perfect or reference quality sound, you simply won't degrade the crap you pump into the cables any further. One thing that is imporant to note is that even the most steadfast engineers seem to favor good cables, they just don't believe in going past a certain point (i.e. recording studio reference cables vs. Opus). There are always the people that hold the opinion that Radio Shack cables are as good as anything out there and everything else is overpriced and over engineered. Certainly the law of diminishing returns applies up the whole spectrum but I'd advise doing a self evaluation and consider the level of cable quality your setup warrants and you can afford. Second, audition and try some different cables. Your ears and your budget will be the determining factor.
