preamp inverts polarity

The speaker cables are marked differently so you can get both speakers wired consistently.  They are not made of different materials designated only for + or - . 

Are the tires on your car for only going forward?   Reverse the wires and be done with it.

How can anyone hear polarity reversal correctly unless the speakers are phase coherent to begin with?   Many speakers have their tweeters and mid/woofers wired in reverse phase.  That happens because of the nature of the crossovers they use.  Only first order, or full range, single driver, speakers will be phase coherent. Never the less,  the listener may prefer one polarity setting on their DAC by the way the correct polarity improves the bass...  but the upper range will be diffuse when that happens unless the speakers are phase coherent

" >>>>my preamp requires me to reverse cables at the speaker end, by design my speaker cables have designated cables for negative connection and positive cables. the positive and negative cables are of different compositions by manufacturer design.<<<<"""""
An amplifier’s terminals are "push pull." They are marked red and black so you can get both channels hooked up the same consistently. When a preamp reverses polarity? Now the positive terminal will be pulling when it normally would be pushing. So, who ever designed that cable with its unique negative run? It is a marketing genius for the uninformed. For, at any moment while playing music the direction of the current in the speaker cables can change directions! Its what controls the speaker movement... There is no one direction for each leg of the speaker wires. They share in moving current back and forth. One second a terminal can be pushing. The next split second on the same terminal the direction can be reversed.... There can not be a dedicated cable material for the side that gets called the negative side. For it shares in pushing and pulling the signal.

Phase coherent speakers only offer a potential.  If the speakers are not set up properly its a wasted proposition. Set up is essential. Its like wearing eye glasses.  If one lens side is angled upward slightly, and the other lens is straight ahead... your eyes will tire you out.