Unless you routinely redline it, I suspect the ASP1000 module is overkill. Max power limit is 30 seconds in any event.
My ASP500 moduled amp looks IDENTICAL (exterior) to the W4S and was made, I suspect, by the same folks. I'll trade my 60second full power time limit for the 3db theoretical headroom increase.
I've never seen over maybe 10vac at the speaker terminals. Even given my crumby DVM from RadioShackup, I'd say no more than 25vac...or about what? 125 watts peak.
The ASP amps have more in common than startling differences. My amp has a 'gain cell' frontend and is a PSAudio. Bel Canto makes a few PS changes.
Maggies are generally a low sensitivity 'easy' load. Most any amp of power sufficient to power them to however loud you like it, will work fine. Better watts, however, trump more 'worser' watts.