Recommended amplification

Interesting topic and one I’ve wondered about. I have the meters on my Accuphase amp set to freeze at the highest wattage during a listening session. Even listening to Mahler Symphonies at 70 db I never exceed more than 1 Watt. My speakers are Harbeth C7ES-XD at 87db efficiency and 6 Ohms and my amp is rated at 150 Watts at 8 Ohms. So I have plenty of reserve power.  I guess I could gave been fine with an amp at half the power. 

Remember, it is not only the raw power output specification that matters.  Impedance matching of components in the amplification chain (preamp, phono preamp, and power amp) and slew rate are critical.  Assuring the amp can handle the low impedance spec of the speakers is also critical.  Impedance matching affects sound quality by permitting optimal power transfer which results in less distortion, a clearer sound, more impactful bass, and improved staging over a mismatched system. Slew rate, or how quickly an amplifier reacts electronically to rapid changes in input signal impacts distortion and dynamics in compositions with fast changing and dynamic passages/phrases. Finally, amplifier quality has an effect.  My most recent experience in moving from a respected but vintage 300 WPC amp to a 105 WPC modern high quality integrated was significant improvements in all areas of SQ and no losses, including dynamics, staging, and image density.  It just so happens the more modern integrated has a higher slew as will as modern design and better build.  Two caveats:  

1:  specification are for designers: use you ears. 
2:  in general, I agree in the most part with all who stated greater power provides more musical authority … most of the time … but other factors enter into the game as is my experience with my recent change .  

Power and listening level are tricky. A 3dB increase in listening level is often referred to as a just noticeable difference...but it requires 2x the power. A 10dB difference in listening level is subjectively twice as loud...ye requires 10x the power. And then we come to peak to RMS levels. With non-compressed material a peak to RMS level of 10-15 dB is often found - which requires transient power 10-30x the average level. So the peak requirements at higher listening levels can quickly escalate.

I don’t think you need 200 watts for the 3a Signatures in that size room.  But I think those speakers like more power than 10 watts. I have them and they sound better to me with more power - particularly with high current amps.  The bass is more controlled and everything gets a little more detailed.  They’re great speakers and you van get more out of them with a better amp.

Thanks for all your input.  I appreciate it.

Question to those who say more power equals better sound:  Could the differences you heard going from a low wattage to a high wattage amp just be atributed to the different manufacturers voicing their gear differently (assuming the increased power wasn't from the same company)?  Has anyone gone from a 25 watt Pass to a 150 watt Pass from the same era?  Or any other company that produces a broad range of the same power amps with the only difference being their wattage?