Ma1746, it is starting to sound like (pardon the pun) there is something wrong with a driver.
And Bro T is probably right, it will likely take a trip to your dealer to sort it out.
I searched for that Denon model, and it is not that powerful; in fact, I could not see any specs for how much power was available all 7 channels driven at the same time? But it looks to be rather low, and low power amps can be driven to clipping when you play music loudly.
And clipping is a speaker killer. That is why most like to have a lot of power available, even though it is hardly ever all used.
Course I could be totally off, all wrong, it is hard to tell without actually hearing it, perhaps even looking at the midrange drivers.
I hope you get a good solution soon.
God Bless,
Wayne

Driver failure is overdrive failure (99.99% of the time), usually by underpowered amplifiers. If the driver(s) are damaged you will want to re-visit your use of the system vs. your equipment.

One easy test is to hook the speaker up to another channel (left or right main) and play some music on the speaker. If you hear the "distortion", then take it to your dealer for evaluation and repair. If not, then it is likely related to your receiver.

And yes, an 80Hz crossover still yields significant mid-bass output.

Thanks for your response. To be clear, the “distortion” or whatever I’m hearing, has only happened twice. It’s a very audible buzzing/crackling sound only on the deepest bass part of a movie scene. And the weird thing is, it’s not heard on every deep bass scene. I ran my speakers through a ton of high volume torture tests yesterday and still couldn’t get the sound to replicate outside of a couple very specific scenes. When I turn the master volume down it definitely lowers the distortion on one scene and removes it on another.

I also switched my front left and center speakers to see if it was an overall power issue. When I played the biggest culprit scene (a plane fly by on the sully atmos 4k disc at -5.0db from reference) the distortion disappears when I have my center plugged into my left channel and my left to my center on the receiver. Both crossovers are the same: could the distortion going away in that scenario be because my front left triton 7 goes lower than my supercenter xl? I don’t really think my center is damaged because it sounds fine outside of these specific scenes.

Yep, sounds like it is not the speaker. Probably receiver's center channel amp clipping, try a 100Hz crossover for the center.

At least you have a repeatable scene to help you trouble-shoot the issue. It's odd that the problem goes away when you feed the front-left signal to the center speaker, and vice-versa. That would seem to rule out an amp problem, bit it is far from definitive. The SC XL could present a harder impedance than the front speakers do to your receiver.

You could try disconnecting all your other speakers from you receiver so that only your center channel is being powered and rerun your test scene. If the problem goes away, that would be indicative that your amps are being over-driven and the speaker is blameless.

Otherwise, ditto the recommendation to bump up the x-over for the SC XL until the problem goes away. If it goes away at 100Hz, just live with that setting. If it doesn't go away until 200Hz, you have a problem that requires further investigation.