I agree with Trell above.
It's not just a matter of XLR vs. RCA cables. It's really about electronic gear that have the built-in differential circuits needed to be "fully balanced". For XLR connections to offer an audible difference over RCA, two conditions must exist. 1) If, both ends of the cable connections are fully balanced, and 2) If there is enough existing electromagnetic interference (EMI) or radio frequency interference (RFI) noise. These types of interference are common in live audio or recording studios, but rare in a home.
Balanced connections are commonly used for live audio and recording studios for microphones with long cables. Long cables (30 feet or longer) carrying microphone voltage level (1-3 mV) signals can pick up noise induced by EMI or RFI. Balanced connections along with the differential circuits required on the electronic gear can cancel out this noise.
en.wikipedia.org
It seems that balanced connections have become fashionable for preamp-to-amp connections, and many examples feature these as a sought-after feature, usually at higher prices. The voltage levels between preamps and amps are in the range of 0.1 to 5.0 volts (100 to 5,000 mV), much higher than microphone level voltages. Interconnects at this voltage level are less sensitive to EMI/RFI induced noise, especially if they are less than 30 feet long. I think that standard RCA interconnects between a preamp and amp are fine, unless you have an unusually noisy environment with high levels of EMI/RFI.
It's odd that people focus on the connection between a preamp and an amp to use balanced connections. This is where the signal level is the highest before final speaker-level amplification occurs. This subject, like so many in home audio, has become unnecessarily controversial because most people don't understand what's really involved.