I use a relatively modest (compared to yours) combo of the Luxman CL-38uSE preamp and MQ-88uC amplifier. They only have RCA connectors so I use those and am in love with the sound my system makes.
Prior to these I had different models from McIntosh, Audio Research, Parasound, and others. Many of these had options for XLR and RCA so I usually went with balanced. It never really made a huge change though. The differences between RCA and XLR seemed more dependent on the specific components involved and not any inherent superiority from XLR over RCA. Sometimes it was a small improvement, other times no improvement at all.
My point here is that I wouldn't worry too much about it. The differences between models of cables is probably more important compared to the XLR or RCA choice.