Hey Tyson, and welcome! It sounds like you're off to a great start. Regarding running the Infinity as a second sub, I say if it sounds better than the SVS alone, then go for it.
As you can see in my sig I've got a pretty decent Paradigm sub and a crappy JBL. Because of my room layout, placement of my subs isn't optimal. Having both subs volume-matched, time-aligned, and room-corrected really helps even out the response so I don't hear bass more in one ear than the other. I lean heavily on the Paradigm for bass below 30Hz, but having both play above that helps. Bear in mind that I never listen at or near reference levels. Your mileage may vary. But with that Denon's Sub EQ XT, you're already set to run dual subs, each with independent correction. You're already a step ahead where I was when I started with dual subs.
Worst case scenario, you try it, it doesn't work out, and you go back to using the SVS only. No blood, no foul.
Depending on placement of the subs, you might need to dial one of them out of phase about 90° to keep them from cancelling out some frequencies.
Sent from my LG-VS980 using Tapatalk