How much power needed to drive 91db speakers?

I drive a pair of ZU Audio, Omen Def Supremes with a Pass Labs XA 25 class A amp. The speakers are listed as 98 db sensitive and I am using my PS Audio Direct Stream DAC as a volume control (probable not optimal), the room is 24x21x8 and I do have 2 Rythmic 15” down firing sealed subs, my listening position is 12’ from speakers. I can reach 100 db sound levels at my listening position. As someone mentioned above Pass labs may be an outlier when it comes to power rating their equipment. Conclusion I listen to mostly rock and the wife will crank up the Techno(feels like I’m in a German Discotech) while working out and I have never wanted for more power. 

As others have said not all watts are equal- I was dumbfounded by an ARC VT-80 that was rated at 70 watts. It was more dynamic, finessed and detailed than several amps rated at 400 watts or more. 
 

Ideally try and get a demo with your equipment - ideally at your house. 

@billstevenson 

"Ask yourself what is it you really seek to learn."

I'm curious. Did you watch a lot of "Kung Fu" when you were younger?

As others have mentioned, power requirements also depend on the size of your room & volumes you enjoy. In addition, the type of music is a consideration. Quieter acoustic music generally uses little watts but music w/ big dynamics and / or big bass can use 10 times the average power on peaks which is the primary reason for truly needing hundreds of watts/ channel. 

@curiousjim. Speaker power requirements see here. 

Mike