winders
Headphoneus Supremus
Well actually the point of using a balanced setup is to eliminate crosstalk between channels created by the fact that both channels share a common ground (also xlr also allows you to run much longer distances due to higher voltage and redundant hot channel which cancels out interference). By using the 1/4 output, you go back to a common ground. So yes, you negate part of the benefit of using XLR interconnects.
But you don't negate the benefits of the XLR connection between the Yggdrasil and the Mjolnir 2...which was the question. The downsides are for the headphones, not the DAC to amp/preamp communications. The main downside is the SE outputs have less power (yes, I knew about that, tjl5709) than the XLR output.