USB DAC balanced or unbalanced inputs?

If I understand you correctly, your DAC has only unbalanced RCA ouputs? If your DAC does not have truly balanced outputs then there wouldn't be any benefit to connecting to the balanced XLR inputs on your McIntosh amp.

The real benefits of balanced really only happen when both components being connected with XLR cables have balanced differential circuitry.

Your DAC would require both normal and inverted phase RCA outputs (0 / 180 degrees). You would then need a special balanced interconnect that is terminated at one end with XLR, while the other end will have (4) RCA type connectors. In a balanced system the signal sent via the balanced interconnect cable is sent to both of the internal conductors that make up the cable. One of the conductors is fed a "normal" signal, while the other conductor is fed the same signal (only inverted). The third pin on the XLR is the ground. Without an inverted RCA output in conjunction with a normal RCA output you will not be able to achieve a true balanced signal. With both outputs it's doable and you can find the special cables - http://www.ciaudio.com/

Does anybody know if the Benchmark DAC 1 USB which does have XLR outputs has the "balanced differential circuitry" that Davemitchell refers to? I have an integrated that will accept one XLR input and am thinking about adding the Benchmark. Thanks!