That's funny, I seem to remember replying to this post. Hmm...
At any rate, the power thump is inherent to all Tempests. DSI actually apologized for it on the old forum when the Tempest was first released, but evidently, we're no longer allowed to mention it in public, else our posts get deleted. Anyway, yes, it can harm for your preamps, amps, and speakers, and so you should always make sure the Tempest is the first thing you turn on and the last thing you turn off.
It's good practice in general to know the signal path and gain structure of your rig, and make a habit of turning gear on and off in a responsible order: i.e. start-up should always entail turning on instruments first, the mixer second, then checking your levels before turning on power-amps, and lastly speakers... Reversing this procedure on shut-down of course.
And I have no idea why the mods took exception to me saying this previously. Like it's a secret the Tempest starts up with a vengeance? Hell, it's the first thing people notice, usually at the expense of their speakers if not their ears. Just lending a little advice on how to protect your gear and your hearing, folks.
Cheers!