Need 25 foot interconnects

This makes a decent  interconnect.  They choose the gold or rhodium ends

https://www.partsconnexion.com/FTECH-88758.html

These are exceptional  but the gold ones that are half the money are really decent  as well. These are really silent 

You’re getting some bad advice here.  As one respondent correctly said, unless the amp and preamp are both fully balanced, XLR’s do you no good.

For DIY, I recommend NeoTech NEMOI 3220.  Single crystal. OFC.  Can’t be beat at the price.  Not cheap but cheaper than finished cables of that quality.
 

Cables are VERY important if you’ve got anything better than entry level equipment.  Put some quality RCA’s on them and you’ll thank yourself later.

If you were starting wtih a preamp with differentially driven outputs, and an amp with differential inputs starting with XLR cables would make sense.

I use the term "differential" to mean the + and - terminals carry equal and opposite voltages. Some preamps or amps have fake XLRs.

Anyway, lacking this, the RCA to XLR conversion is an opportunity to introduce noise and distortion in the line, so best to be avoided if possible.

@dougthebiker 

That's not entirely true you don't need differentially balanced equipment to have balanced outputs and inputs, it can be single ended inside the circuit in the equipment and you can still have balanced inputs and outputs, there are a few different ways to do it a transformer is one way.