W4S ST-1000, How Loud Should It Play?

ICE amps......virtually all the ASP module amps are strictly time limited at full power.
The Wyred amps are near-clones of the PSAudio offerings of a few years ago.

http://www.icepower.bang-olufsen.com/files/solutions/icepower1000asp.pdf

NOTE: the 15 seconds at max power and the fairly low FTC power rating, which is 'continuous' per FTC testing procedure.

If you require, as average power, more than the amp is capable of, you may simply need to upgrade to something with more......real power....
Perhaps Bryston or Pass?
I own a 'd' amp, so I'm user. At 90db output to my listening position about 11' from the speakers, I measure about 20v to my Magnepans. The peaks must be much higher, but I don't have a scope or peak capture meter.

Al,
Right you are. And from a personal standpoint, I simply NEVER play my panels loud enough to get 'slap', what panels do when they bottom out.

You also bring up one of the really big differences between commerial sound gear and home audio. Professional sound reinforcment speakers can take the kind of pounding which reduces home speakers to junk.

My ICE amp never gets more than warm to the touch. More a tribute to my moderate habits than any inherent high efficiency. A couple kilos of heat sink would probably really help the FTC power.