7500 for USED cables? Are they joking?

Signal interference is the key word here. You are asking the wrong question!

>>>My question stands. How is it that designer cables improve what goes into a recording via cheap generic cable? But this is just food for thought. I really don't have an answer, or for that matter a dog in this fight.><

It is true that no cable can improve what the sound engineer messed up or not, but this is not the job a cable is supposed to do in the first place.
The job of a cable is to the transmit the signal as pure as possible and do this with the least possible amount of loss or interference. So it simple words: An inferior cable will interfere and degrade the sound to a greater extend than a superior one.
Without wanting to promote HMS cables her, Mr. Strassner of HMS, who like "vanservers" is an engineer and holds a PHD in atomphysics, discovered, that i.e. the magnetic field plays an enormous role, how pure the signal is being transmitted inside a speaker cable. The more the magnetic field has a chance to escape, the more the sound will degrade on its way to the speakers.
So some of his designs have to do with containing this magnetic field inside the cables. You can imagine that a cable like this will be much more expensive just to build, than taking a few feets of Radio Shack wire. And this is only one of many factors he has dicovered, which play a vital role in cable design.
Its not so much what goes into a cable, but what comes out of it and what has happened to the signal inside the cable.
Compare it to your own body: There is a disease which will interfere with how well food inside your guts is being absorbed. Two persons eating the same food, one will stay healthy, while one will die.
And you need the necessary resolution of system to display these differences also
Let me give you another example:
Let us say you have one of the high resolution digital cameras, which will give an incredible detail richness. Now you plan to print the picture and you have a cheap printer with limited resolution and a high-res printer. The photo file is the signal and the printer is the cable. So, altough in both cases you have the same photo file (signal), the print (sound) will be much more detailed when you print it with the high-res printer (cable)
So, at one point, it really makes sense to think about buying better cables for a system. But I agree, some of the prices are outrageous, which led me to my personal cable quest and ended in having found the HMS cables, with a wonderful price-performance ratio. The HMS cables are not cheap, but they do not carry these gigantic price tags, some of the companies carry, either.
One company recently came out with a new alloy, which is used in Germany for teeth fillings (because its so cheap) and their 8 ft speaker wire will cost you $15.000,00. Now this is a stiff price tag, if on the other hand, you can get a wonderful cable with mind blowing performance for one fith of this price, as I have personally discovered. That is the only reason I even dared to become an importer of said cables. But even this is a lot of money, but alas, good quality will never come cheap, but it does not need to cost so much either, that you have to apply for a second mortgage, when planing to buy a set of high-res audiophile cables.
The only advice I can really give you is, to ask any cable manufacturer for a money back guarantee.
Try to narrow your choice down to a maximum of 3 different brands and then try them out, in your system and be your own judge.
I mean, it will be your ears listening to your new cables and not the manufacturer's ears. And if these guys are honest traders, they will give you back your money and you havn't lost anything, but gained valuable experience by auditioning different cables.
I have listened to almost 50 brands of cables during my quest and over the months I was really able, with the help of Chesky Records test cd's, to improve the ability of my audiophile hearing. And I really mean a lot. And believe it or not (btw, we have a Ripley's "Believe it or Not" museum her in the FL-Keys) there are differences in how cables sound. So there should be some examples on display there for people who still will not believe it...or not???

Are there hi-res cables? I think there are cables with a high resolution factor. On Chesky's sytem test disk, there is one track called the high resolution test. Shakers in the background are supposed to sound differently with every shake performed.
With my HMS cables and the Valhalla, there was no problem detecting this minute sound differences.
Then I went to another cable, which was not cheap ($850) but now it was almost impossible to detect the differences in detail.
Not only was the high-resolution gone, but also the mid- range purity had kind of suffered, the other cable sounded somewhat somber and dark, veiled if you like.
Mr. Strassner of HMS was a big doubter himself, believing that every cable with reasonable performance will deliver, but one day he was given the chance to listen to an excellent cable in an excellent system. That was the day of revelation, and according to him, he set out, with the help of his technical expertise, to see what was causing these differences.
His whole design ideas are created around the knowledge of the impact of the magnetic field and interference of EMI/RFI and some other discoveries regarding the dielectric. The impact on frequency responses is only one of many factors.
Basically one of his biggest inventions is to keep the magnetic forces, which are created in every electric conductor, inside of the cable. He does this with ferrite blocks made out of a special alloy.
Well, he has his ideas, Nordost with the Valhalla have their secrets, but in the right system, both cables make an incredible difference.

Marc, I have been using a cable burner for quite a while now (Audiodharma, made by Alan Kafton) to break in all the cables, before I send them out to my customers.
Since I had chance to audition more than 50 different brands of cables, I can tell you, it made always a huge difference before and after.
I am putting again a brand of cables to the test against my HMS cables and the day I got my competitors cables, I put it straight into my system. They sounded quite edgy, metallic, if you want. After two days on my cable cooker though, it had vastly improved.
Now I was able to conduct my private little cable shoot-out, to see if other cables can best the price-performance ratio I have found in my cables.
(Since I do not want to bash the competition, I do not say names here anymore) but as you must be aware of, I have done some rather bold statements regarding HMS cables, which, up till now, still hold up.
So yes, in my opinion a cable cooker is a wise investment.
Talk to Alan about it (I am getting no provision here). He will explain everything much better than I can. But for me, a cable cooker works.