Did I blow my D2000s?

Another possibility is that you are hearing the sound clipping in a recording that's too loud. I know I get crazy clipping on some tracks. If you have another high quality pair of headphones, listen to the same tracks and see if you hear the same thing.

I'm not hearing any kind of obvious stuff on that track, at least not with my Beyers. You probably do have some sort of issue somewhere in your setup.

No you didn't blow your D2000s.
The crumbling sound you describe is in the recording.
Nice song by the way

Make sure your PC isn't doing any kind of signal processing, especially things like bass boost or EQ or any kind of audio effect.

Go into Control Panel >> Sound
Check the properties for the sound device you're using. Make sure nothing like bass boost or EQ is enabled.

Make sure iTunes isn't doing any EQ

The sound on that Mumford and Sons clip is already very hot. Close to clipping (if not already clipping on the peaks). Any additional bass boost would almost certainly cause obvious clipping and that type of digital clipping may be what you are hearing as a crumply sound.

That's the curse of good headphones with modern (too hot, loudnessed) recordings. Good headphones will make the clipping more obvious.

One thing you could do just to familiarize yourself with what digital clipping sounds like in the bass. Find a good quality recording with good bass and some bass punch. Something that doesn't already clip. Then play it on the computer while adding bass boost with the EQ. Add enough bass EQ to force clipping. Then you'll know what the clipping on bass notes sounds like. It's probably that exact crumply sound that you're hearing.

Better headphone amps can make the digital clipping in the bass less annoying or toned down a bit, especially with low impedance headphones like the Denon. If the headphone out is already struggling to provide enough current (low impedance headphones need more current from the amp) you may be already getting some distortion in the bass due to the amp not having enough control and power for the Denons. So you'll be getting some distortion and lack of control already before even any effects of digital clipping in the bass. Add the two together (lack of control from the amp and the digital clipping) and you get a double whammy.

I don't know what quality of headphone amp is in the Kenwood preamp you have. Sometimes they can be quite wimpy for the needs of the Denon (and other times quite fine). If it's a wimpy amp you'll get distortion and lack of control in the bass even on recordings that have no clipping.

So find some bass heavy recordings that you can confirm have no clipping and no audio problems with the bass. Listen to them on your kenwood pre and see if you hear any bass problems. If you hear bass problems (worbles, crumply sounds, etc) then the problem is the headphone out on the kenwood pre.

Or as an alternative find someone who has a quality headphone amp that can handle the Denons and see if you get the same kind of bass distortions (that's something you can do at a headphone meet).

I've heard my Denon D2000 distort in the bass due to an underpowered undercapable headphone amp. It doesn't sound good at all.

that's what you get when mixing hi-fi equipment, with lo-fi recordings.

I'm a big fan of lo-fi as well by the way...

If you're getting a lot of crumply sounds with the Mumford and Sons clip I would be strongly suspecting at this point that it's the headphone out on Kenwood pre that is causing the distortion. It seems we've eliminated the digital clipping since you're not doing digital EQ or digital bass boost. There is some digital distortion in the YouTube clip, but nothing bad (by modern recording standards) and not a constant or regularly occurring crumply sound.

The Mumford and Sons isn't low fi. It's hi fi. The complaint would be that its not "audiophile" since it is loudnessed and has lost dynamics and the sense of air and space that an "audiophile" recording can have. It's what recordings are in the current loudness war era.

I'm not going to judge their CD quality based off a YouTube clip. YouTube clips can end up more compressed, boosted and normalized than the audio that is on a CD release. The CD release could be better.

Not consistent. Often nowadays the vinyl version is done from the same master as the CD. So no difference in dynamics compression level. Same sound as the CD. Only difference would be how vinyl playback reacts when trying to play a clipped off waveform compared to digital. A bit of a ripoff for those paying more for vinyl than the CD version.

If they do actually do a separate mastering for the vinyl then you can get some benefits and have vinyl that sounds better than the massmarket CD version.

One band that did that is Mudcrutch (Tom Petty). They made a special vinyl master and the vinyl version came with a special version of the CD as well. Both the vinyl and the CD are quiet with dynamics (not loudnessed). It even comes with a note telling you to turn it up because it is not as loud as common CDs. But you have to buy the vinyl to get that CD version. The massmarket CD got the massmarket loudness treatment.

I wouldn't say the AD900 is good for rock, because it really depends on what type. They don't rally have a lot of bass. I'd keep the denons for hard rock, hard-ish rock, etc. I really enjoy the AD900 for progressive rock (rush/pink floyd, etc.) and older stuff (from -like- the '60s) and they're great with anything soundstagey (I just listened to virtual barbershop again, it's frighteningly good). I haven't tried any indie yet.

But for most rock, I'd go with a grado. That's why I'm saving up for an SR225i soon.