What is the most important cable in your system

@tweak1      Mad, yes.   Scientist, no.

@tweak1 My neighbor has a high end/cost system with YG Sonya 2.3s, subs, Bekerely USB, Meridian Ultradac, etc.  He has high end ICs and speaker cable but was using Pangea power cables.  As an electrical engineer, he didn't believe power cables could make a difference.   His bass was terrible, frequency anomalies where a bass would play one not forward and the next up would be hidden, then in, then out.  Terrible.  

I lent him one older GroverHuffman Empress power cord for his amp and he heard the difference, a smoother frequency response in the bass.   He opted to purchase six GroverHuffman Pharoah power cords.   Now I can sit and listen to his system with pleasure as the sound is coherent, smooth/even frequency response.  He also tweaked his Audio Research SP28 preamp by replacing the 6H30 tubes with 6N6/6H6 tubes.  Sounds great now.  

I agree with the deooney. I have found that the most important cable is the one between the Amplifier and Preamplifier.

XLR cables really shouldn't have a sound. 

I have a system that has evolved quite a bit over past 7 years with a variety of amps and speakers, in and out of the system.  My dac, streamer, server and power distribution have all stayed the same.  

And while I’ve noticed subtle changes as I swapped out and upgraded all of my Ethernet, XLR and speaker cables, the biggest difference I have found has been power cables.  Most recently, upgrading from the Audioquest Firebird HC to a Dragon HC on my integrated amp has produced the most profound improvement I’ve ever experienced from a single change.  And that includes both cable and equipment changes.  It’s like a different amp.  

Must be synergy, but I never expected my system to improve in so many ways without any downsides…and I say this with equal conviction today as the day after I first introduced the Dragon HC to my system, and that was about a month ago.

As always, YMMV but I’m still stunned by the improvement.