After looking at the photo of the Yiggy’s internal printed circuit board at the Schiit website I think it is very likely that the two RCA outputs are simply wired together, and using both of those outputs would therefore be not much different than splitting a single RCA output externally.
It is also very possible (although I have no way of knowing for sure) that the signals provided to the RCA connectors are the same signals that are provided to one of the two signal pins on the XLR connectors. That is done in many designs which provide both RCA and XLR outputs, and in those cases using the RCA and XLR outputs simultaneously is likely to be a less than optimal approach.
Also, the Yiggy’s outputs are described as having a low 75 ohm output impedance and being suitable for driving 600 ohm professional gear. This suggests that using its XLR outputs to drive two components would not be an issue.
Given all of that, I suggest purchasing a pair of one of the pro-oriented and inexpensive XLR y-adapter cables shown at
this link and giving them a try.
Regards,
-- Al
Thanks Al, they look perfect for my intended use.