Best Location for Best Cable

I have an all Benchmark system, DAC3B + HPA4 preamp + AHB2 amp + Benchmark speaker cable. I am using Benchmark StarQuad XLR interconnects on all the above components. The HPA4 + AHB2 is separated by about 15 feet so I have either a 15 foot or 20 foot XLR between them. System sounds excellent.

Today, I received my upgraded Audience AU24SE (some XLR’s and some RCA’s, all short) from Audience AU24 and AU24e. I put the AU24SE XLR between the DAC3B and HPA4 preamp and notice a very slight unveiling of the sound. It sounded even more excellent now. I am not even sure if the Audience cables are burned-in because they are upgrades not new (likely burned in).

I am now wondering where the best bang for the buck improvement in cable sound comes from. Is it the sources connected to the preamp or the preamp connect to the amps? I cannot permanently move my gear around anymore since I have committed to my current setup, which I love. I have a new stereo rack coming next week and it is too big to put between the speakers to have the preamp and amp close to each other. I am also not sure if non-Benchmark XLRs would work great sonically for very long lengths with my gear (cost is also a factor).

I am just curious as to where people put there best cables. This info will be useful to see what I should try.