I have been through this several times testing my Wadia 321 DAC as a preamp as it is balanced as well as the power amp. But my Mullard Rogue RP-1 only has single ended. Even with Balanced and some relatively nice XLR Audioquest cables the system always sounds a touch better (smoother) to my ears with my tubed pre in the mix.
About once a year I switch back to the Wadia pre only to return to the Rogue.