The rule of thumb is to break between the preamp and amp, so long interconnects and very short speaker cables. It is ideal to put mono blocks next to the speaker they power. You get a big performance gain with 1 - 2’ high quality speak cables. The shorter the better.
XLR is not required for that length… but they certainly will not hurt and may help. But if it is a trade off between much better quality interconnects and XLR I would likely choose single ended.
If you have short interconnects (both rca and XLR) I would compare them and see if there is a notable difference. While my preamp and amp is of balanced design and the manufacturer recommends XLR… I could not hear a difference.
That being said, I bought XLR because I could afford them ($5K) and it was worth the piece of mind. But it is up to the individual. Going from RCA to XLR was nearly $3K more.