Where to put best interconnects

If you have one very good new set of XLR cables and one older but still good set, the best placement depends on your system’s signal chain. 

Between the Source and Preamp: This is often the most critical connection because the signal is at its lowest level before amplification. Any improvements in shielding, conductivity, or overall cable quality will have the most noticeable impact here.

Between the Preamp and Power Amp: The signal is already amplified at this stage, so while cable quality still matters, it may have a slightly reduced impact compared to the source-preamp link.

Start by placing the better cables between the source and preamp and evaluate the sound. If the difference isn’t significant, try them between the preamp and power amp.

Let your ears decide!

I use Audience AU24 SE on my sources to my preamp. I use Benchmark XLR's (25-feet and 15-feet for 2 systems) between my preamp and amp.

The preamp to amp connection did not benefit with the same Audience AU24 SE XLR when I tested it out by moving the preamp near the amp for testing.

Best interconnects on amplifier. Best power cord on amplifier. Then work your way up the chain.

Will place the better cables at source, according to Lalitk.  Have SR Atmosphere Eurphoria SX as the newer, and Transparent Reference from 2003 as older, which are ok, but not as revealing.  

I’ve found that both the cable between my dac to preamp and preamp to amp make a difference. I’m using the same cable type for both. I couldn’t say which one is more important.