What do audiophiles want from a cable?

Yes, I believe it true that different cables each have their own sonic signature imparting their characteristics in your system. For example, I used to own a Theta Pro-Basic 3, and it was very aggressive, however by inserting a mostly entry level Cardas cable, it completely calmed it down. The Theta and Cardas are no longer in my system. I for one believe in symmetry and also believe you do not need to spend the same amount of money on an IC as you spent on the source component itself! My system currently is Kimber Silver Streak throughout, Balanced and SE, there are better sounding cables out there, but I either can't afford them or the price/performance ratio was not there after audition. I think finding the balance between cost and performance is a hard thing to accomplish. There are some great values out there often overlooked because they were so inexpensive they must not sound good?? Here again, I believe there are diminishing returns as cable price increases and I also believe in not "drinking by the label". In the end my belief is there is a VERY loose correlation between the cost of an IC and how it performs.   

Waxwaves, I never tried any Proteus or Dominus. Also, your system is very different, so no wonder it requires different Purist cables for the overall best sound. But I can tell that another striking quality of the Neptune fluid is its great balance, nothing is exaggerated or diminished, and it is neither forward nor laidback, great dynamics and details too. Unlike Colossus and Maximus Ferox RCAs, the former slightly exaggerates high frequencies and the latter - bass. But I must add that as it was designed, both Colossus and Maximus were fluid cables, replacing fluid with Ferox threw them off the balance a little. The Colossus fluid speaker cables are in my opinion better cables and work great in combination with all copper Neptune fluid. In time I will replace both Colossus and Maximus Ferox interconnects, I am just not sure with what yet. Probably original fluid Ag/Cu/Au Dominus or another Neptune would be best though slightly different choices. Just try to find used original Dominus, almost impossible.

Only two things are required:

Resolution. Everything that comes in goes out again. Unchanged.

Linearity. Resolution is the same for the entire audio frequency range. 

The better cables maintain these characteristics with a variety of components.

Inna...yes all systems are different in one way or another.  How is mine very different?  Just curious...

 I feel like the Jade Audio cable sounds a bit better from the Lampizator than Venustas does.  But PAD excels between preamp and amp, and then again as speaker cable in this system.  I've experienced best results with the last legs of cabling being the same.  I can take the excellent foundation that PAD lays there and mix the qualities of the Jade ic, the WyWires USB cable, etc to get the sound I'm looking for.  You see where I'm going with this.  The full loom of PAD is still solid and well balanced, it's good stuff.  Just kinda bland and lacking the liveliness, attack, and refinement in the upper end of the frequency range that WyWires or Jade cables bring to the table.  

Sounds like you also enjoy the PAD cables Inna.  Yes Dominus are incredible and had me drooling over the emmense soundscape.  Dominus are out of my reach at present.  If I had a loom of Dominus, my opinion regarding the mixing of cable brands might change Inna.  They are certainly special and there's no denying it.

imjerrys, does all that linearity and perfect resolution ever get boring, sterile, overly analytical?  I hope you are not trading off full bodied musical sound that is harmonically rich?  It's so hard to have both in this hobby.

What most audiophiles want from a cable is confirmation bias.