Is tonearm cable the most important cable in the system ?

@hifiman5 Good point.  Your cables should be treated as a component itself.

Yes of course every cable is important but not necessarilly equally important in each particular system. Often the closer to the source the more important. I am not talking about power cords now.
When upgrading, most of us cannot afford upgrading all the cabling at the same time, especially when doing serious upgrades.

Leeds - I wonder.... where exactly would you get a seperate ground reference for left and right channels in order to run a "truly balanced" XLR cable from a phono cartridge that has only 4 pins (left/right +/- )????  Stereo Phono cartridges are INHERENTLY balanced devices no matter what connector you happen to be using at the phono stage.  

jwpstayman

... I wonder ... where exactly would you get a seperate ground reference for left and right channels in order to run a "truly balanced" XLR cable from a phono cartridge that has only 4 pins (left/right +/- )???? Stereo Phono cartridges are INHERENTLY balanced devices no matter what connector you happen to be using at the phono stage.

You’ve answered your own question - a phono cartridge is inherently balanced. If you connect it to a properly balanced differential phono preamplifer, the cable will be much less critical - that’s the nature of a balanced circuit. As for XLR cables - I never mentioned them. As you note, you can have a balanced connection regardless of the connector. In this instance, you get the separate ground wire from the pickup arm - almost all pickup arm cables include the separate ground.

The issue with the tonearm cable is the extremely small cartridge output voltage traveling through it. Noise pick up (no pun intended!) can be a serious problem. A shielded cable is a real good idea.