what's the most vital cable in a system?

There's an old audiophile saying; "The best a system can sound is related to its weakest link". With this in mind, there may not be a valid answer to your question. Try not to skimp on any one given connection, this will probably give you the most bang for the buck. A final point, trust YOUR OWN ears, when you make those cable comparisons. There are quite a few "recommended" cables, that are real stinkers (especially, if you factor in their cost). I have making my own cables (based on a design involving 18 audiophiles and 3 electronic designers), which sound better than cables 10x their cost, i.e. IT DOES NOT TAKE HUNDREDS AND HUNDREDS AND HUNDREDS OF DOLLARS, TO PRODUCE AN EXCELLENT SOUNDING CABLE!!

I agree with Ehider that the system is only as good as the weakest link. However, with all the components in a system being comparable, I would say that the cables closest to the source is the most important, then from preamp to amp, then the speaker cables. If you think about it, if you use crappy cables between the source and the preamp, no matter how wonderful the cable you use between the preamp and the amp, the sound is already degraded or colored. You will just be producing accurate sounds of what your cheapy cables produced. Work from the source-preamp to preamp-amp to speaker cables.

My understanding is that the lower the voltage a cable carries (line level) the more prone it is to EMF/RFI. This seems logical because microvolts can be more easily disturbed than 'macrovolts', so it follows that good interconnects are 'more important' than speaker cables. That said, I think the question is a conundrum and somewhat like asking which wheel is the most important on a motorcycle. Both front and back have an important function, and regardless of how good one is, without the other, it's virtually worthless. The efficiency of any system or process is determined by the weakest function within that process (as stated by Ehider, above), and you would be well served to follow his(or her) advice on trusting your ears above all else. Good luck!

Kweisner, if lower line voltage cables are prone to more EMF/RFI, how seriosely are the conections fron power supply to unit affected? Any thoughts on how to improve or upgrade? P.S. I also believe you start at the source and work down the chain. BUT DO UPGRADE!!!

All of the cables are vital 'cuz the system won't work without them :-) Out of curiosity, what is the rationale for the interconnect from preamp to amp being the more important than the interconnect from source component to preamp? When I upgrade interconnects, I do all the line level interconnects in one fell swoop (or is it swell foop? whatever...) I think that if one considers signal levels, driving source power involved, and susceptibibility of the receiving end to cable-induced signal degradations, the hierarchy of cables having most effect to least are: (1) low level analog interconnects such as from turntable to phono amp (2a) line level analog interconnects such as from CD player to preamp, DAC to preamp (2b) line level analog interconnects from preamp to amp, (3) speaker cables, and finally, at a very long distance behind the others, (4) AC power cables and (5) digital cables, the latter especially for having insignificant incremental effect once basic electrical performance specs are met. It also seems that (4) and (5) are subject of much more mystery and heated debate these days than (1), (2), and (3). This observation is consistent with the First Law of Audiophile Discussion: heat of the debate is inversely proportional to size of the effect :-)