Tube amps and rock music...

I am using two, no-name, 60wpc tube amps and when I put on some classical music, it sounds really good to me, but when I put on some ACDC, it sounds like sludge, really slow, and sloppy. Is it just my tube amps or is this the case with tube amps and rock music?
Must be just your amps. I have an ARC VT 100 mkII and I can enjoy jazz, rock, or classical. Bass is good and tight, not pudgy and slow.
What speakers are you using? If your using lower sensitivity/efficiency speakers, you may have a problem with more demanding source material. Also, powered subwoofers work better for bass than most conventional passive speaker woofers(ported or otherwise). Still, a lot depends on the speaker design!
I would suspect your tube amps would sound really powerfull on some very sensitive horn speakers with big bass drivers. Or driving some speakers with powered woofers, or potentially some small monitors crossed over to a subwoofer!
If you're driving difficult full range speakers, of lower sensitivity, and possibly impedence, you may have problems getting dynamics out of em.
No problem with heavy metal on my tubes.