What you describing sounds like either lack of seal, or earcups not positioned correctly, or a weak clamping force.  Keep in mind, these are not over ears but on-ears, and sometime you need to adjust earcups to find that sweet spot.  Also, maybe the headband is stretched to the point where clamping force is down to minimum.  Try to bend the headband and hold it together to tighten the shape.  As you mentioned, hundreds of people who reviewed or commented about XS where happy with a bass and I'm sure you didn't find anybody else sharing your experience.  Not arguing that you are not hearing the bass, just suggesting that something might be off with your pair.  Btw, do you get bass when you press earcups against your head?

Yes - there's clearly something not right here. I've experienced eyeball jarring bass with these when listening to EDM type stuff, and warm, percussive ear-honey when listening to classic Rush, for example. And there's nothing lacerating about *any* frequency... voices and snares actually sound like real voices and snares. If anything, they're quite polite; smooth, warm, yet flat mids, and open, airy highs that I do wish had a touch more sparkle. In fact, I'd say these have as much bass as my M-100's did, but without the tubby bass resonance. I actually think you may want to send your XS back and get another XS... something may be faulty with the unit you received.

I'm voting for the defective pair theory. I have the M-80s and would even describe them as bass-light. From what I've read the XS are supposed to have improved the bass!

I have three sets of portables in this tier (m80, dt1350, amperior). M80s get the most head time and go with me when I travel.

*would NOT even

These do not have as much bass as the M100. They will not rattle eyes. That kind of lingo leads to 2 star reviews because little words get taken seriously by the public.    To the reviewer: A 40mm driver does a lot of good things but a 50mm driver can do more particularly in bass impact.

Again, I was mentioning my experience - listening to Haywyre's "Sculpted" at an irresponsible volume made my eyes vibrate to the point that I couldn't focus. So that kind of lingo is used because it happened, not simply for effect. So, yes, they will rattle eyes. Please don't assume you're me; feel free to list your experience but stop exercising your psychic powers

Yep, think you may have a defective pair. Only some advise... The lp's will not only rattle your eyes but your spine. The bass is way over powering so much so the ear cups actually vibrate.