Not a silly question, even though the manual for the DS Jr. states that "it is fine to use both outputs at the same time," referring to the RCA and XLR outputs.
I looked at the manuals and descriptions of the DS Jr. and the KRC-3. The relevant impedances are not suggestive of an impedance compatibility issue when using both interconnections simultaneously (even if the signal provided to the DS Jr.’s RCA output connector is the same signal that is provided to one of the two signal pins on its XLR output connector, as is done in some designs), although the input impedance of the KRC-3’s S3 input when configured in HT bypass mode is not specified.
Given that, I doubt that using both interconnections simultaneously is having any sonic consequences. Although I suppose there is a **slight** possibility that if the DS Jr. is designed such that the signal provided to its RCA output connector is the same signal that is provided to one of the two signal pins on its XLR output connector there could be slight adverse effects on the noise rejection performance of the KRC-3’s balanced input, due to the slight impedance imbalance that would result between the two balanced signals. And perhaps also due to the introduction of differing amounts of noise on the two balanced signal lines.
It’s also **slightly** conceivable that signal "crosstalk" could occur within the KRC-3 when signals are provided to both inputs, that would be great enough in degree to have audible consequences, and that would not occur if only one input is connected.
As I say, though, I think it is unlikely that any of these possible effects would be audibly significant. But the way to be sure, of course, would be to simply disconnect one pair of cables (while power is turned off, of course), and see if that makes any difference in the sound when using the other pair.
Regards,
-- Al
