Sure wish someone would have pointed out Y cables before I spent all those thousands of USD on all those audio DA's in my production truck. Looked in my interface box, no Y cables. Hmmm.
Seriously, there is always the issue of s/n and hum without any isolation. And an aside, we use all balanced audio in the truck and are in the process of going with fiber, no more copper (for audio or video). Exception, the 3 ph power mains.
Can't push many hundred amps thru fiber. Too much of a load.
Plus impedance isn't just resistance but combined with the effects of reactance as well. Then there's lead length and routing assuming shielded/screened. Thought as long as the sound card has extra outputs available for a few bucks, why not use them and keep everything nice and clean?
Why don't we let Luc hook up his sub (quite a few options presented here) while we commiserate over some spiked cider or eggnog?
A little early, but Happy New Year. Imagine twenty nineteen already.
Rgds,
Ed