If you’re using XLR cables, it’s assumed that the equipment it’s connecting are truly balanced. Unfortunately, this is not necessarily the case for all gear. But let’s assume it is for your gear. Then there’s the question of whether or not the manufacturer supports the Balanced Line standard. Unfortunately again, most do not. For the few that do, the balanced cable used becomes somewhat insignificant.
I believe Ralph Karsten at Atma-Sphere would say completely insignificant for those that follow the standard in that you will not be able to distinguish between any reasonably well-made cables. As i understand it, this standard was developed more than 50 years ago and is fully adopted in pro audio which allows them to use cables up to 200 feet without sonic loss (or coloration).
If your amp and preamp follow this standard - you can use any decent well-designed cable and the results will be essentially indistinguishable from even very high end cables - by design. Again - most do not follow this standard. But the closer they get to it, the less impact.
I’ve found this true in my own set up. I purchased very high end xlr cables for my equipment at the time because on audition they made a significant improvement. But with my new preamp and amp, I can no longer distinguish between them when it was remarkably easy to do so with the prior, less resolving gear.
Bottom line - if your amp and preamp do not follow the standard, try it both ways to see which is better. If they do follow that standard, absolutely put the better cable between source and preamp because the former most likely doesn’t follow that standard.
For those that are skeptical of this - I can attest to it. And, I’ve got more invested in cables than most.
