Actually, The Thousand Sons have "All is dust" as their 'warcry'.
So that's Tzeench taken care of, seeing as his posterboys are pretty much the only active worshipping marines.
Not really. That battlecry is highly specific to the Thousand Sons and their history, and isn't generally extensible to most if any of Tzeentech's other followers. "All is dust" doesn't even really extol Tzeentch's ideals. He's not about fatalism and finality. He's about eternal change and the weave of fate.
Not heavy metal?
I think Heavy Metal tends to be about anger and exploring your inner darkness. Slaanesh is all about experiencing things at their zenith, always striving for that next level of sensation. If you've ever been to a rave where people are doing a lot of drugs, it evokes that image, just people wildly out of control looking for the next high, sweaty bodies, throbbing base notes...
Plus lots of people consider techno noise for its own sake anyways
You can probably make the argument for any type of extreme music being representative of Slaanesh in some way. For me it's just techno.
Slaanesh has no particular battlecry, nor do Tzeentch or Nurgle. Some of their mortal servants have battlecries, but none as ubiquitous as 'Skulls for the Skull Throne!'
My friend who is also pretty deep into 40k lore had the take on it that, Khorne is really the only Chaos God of War. He's the patron deity of all warriors who don't worship the other Chaos gods. None of the other gods really take the aspect of the warrior besides him. Tzeentch is a scheming sorcerer, Slaanesh is a sensualist pervert and Nurgle is a fatherly primal force of nature. So it makes sense that of all the servants of Chaos, only one group has a unified battlecry when they go to war. Other Chaos Gods may have warriors, but their warriors don't server
the God of War.