Lee, so the bottom line is that there appears to be incorrect wiring in either one of the Marantz XLR output channels, one of the Sunfire XLR input channels, or one of the BlueJeans XLR cables connecting them. Whichever may be the case, there's already been more than enough concern exercised, so just relax and enjoy the better sound. The coaxial connection is totally sufficient.
The balanced XLR connection is only of benefit in reducing noise in primarily professional applications where there's both a high level of electrical interference and long runs occur through it. Most home setups, undoubtedly including yours, don't experience an interference problem with regular shielded coaxial cables. Reports of substantial XLR benefits, not relating to just noise rejection, exist on some audio forums, but if the equipment used didn't compensate for the double voltage(by having 6dB less gain in the XLR circuitry), causing an increase in loudness at the same setting, this is simply another example of louder sounding better.
Incidentally, both the Marantz and Sunfire units are designed to use the standard pin2 positive convention. Also, the quote from the Marantz manual regarding supposed "methods" is incorrect or at best, outdated. For the correct info on this point, see Bob Lee's discussion
here .
