tonearm cable, do you need one?

You do need a cable that is specific.

The reason is capacitance, something that occurs with any interconnect cable. With a phono cartridge, which has inductance, the capacitance will form an electrical resonance. If its a high output cartridge this might be at or just above the audio passband.

If you don't have a low capacitance cable, the resonance will be in the audio band with that high output cartridge. It will sound peaky and bright. So you need a low capacitance cable, nor more than about 20picofarads per foot. The ground wire is there to prevent buzz from being audible. It is connected to the ground of the arm itself and the chassis of the phono preamp.

+1 what @chakster  said.

Also you have shielded IC's you can run a  separate ground wire using an inexpensive 16-18ga wire

Easy peasy ADD a ground wire. From the source to the phono stage and the phono stage to the preamp... No phono stage! Go from the source to the preamp.. I use good copper... 1.00 usd.. for the GREAT stuff...

NOISE... connect it..

Regards

Thanks Ralph @atmasphere . I think I may have known that but its been a long time since I had an arm without the captive cable. Its good to be reminded of error. But don’t tell my wife I said that. (-:

The VPI cables are made using the same Discovery wiring that the VPI arms are wired with, that is unless it is the upgraded arms with the Valhalla wiring. There are those who believe as I do that the combination would have a given synergy. Enjoy the music