Balanced vs RCA preamp output

It really depends on the equipment being used as the manufacturer may have put more time, effort and money into developing one connection versus another. Some companies may add XLR inputs/outputs to gain market share but they did not spend the money to make that section of the product as good as it could be whereas the RCA circuit is top of the line. A truly balanced system takes more money to make and if they did it right then XLR is the way to go, but RCA or single ended designs are much easier to get right and thus very common. Just because a component has XLR inputs/outputs does not make it a "balanced" circuit.