Re: Apocalypse in 9/8
Not just stress: the actual intervals between the beats need not be constant. This is sometimes called swing.
Them sometimes in compound time beats, commonly the second of each group of 3 may be effectively missed, so instead of (say) 6 evenly spaced beats you have four, but the first of each pair double length.
Related to this you'll sometimes find the first and third beats of 4 time lengthened, occasionally even to such an extent that the rhythym is closer to 12 time with the missed beats as above.
Of rock bands Thin Lizzy were major users of compound time sigs, which is one thing that gave them their distinctive feel. Much mainstream rock is rigidly stuck in 4 time, but Lizzy often played in 6, 9 and 12 time.
Its a very complex topic!