60 WPC sufficient power?

Look for quality first and then try to find the quantity that you need. There's no doubt in my mind that you could go down in power and get better sound without losing much in terms of total SPL. In fact, you might find that with a better quality amp, it sounds much better at low volumes. Then again, i've always found that the better a system sounds, the more likely you are to crank it without it sounding cranked. That's because distortion is minimized, making it sound much smoother and more coherent even at raging spl's. Sean
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Well, I have found that dynamic range and unfiltered amplification are more important than pure power. How else can one explain the musical performance of a Creek amp or single ended amplifiers! Massive wattage is not always the best; it may be the loud but not musical or 3-D.

Many high wattage amps have groups of transistors or tubes in parallel and push/pull pairs. The recombined signals have hashes in the electronic signal. These present themselves as white noise or bright spikes. The need to filter these high frequency spikes can cause losses of real nuance in the music.

So, are you the type to listen to jets taking off in the soundtrack of a movie like "Top Gun" or someone who try to listen for the bell ringing tone that exist in all live performance of a cymbal strike in a Jazz concert?

Can't answer your question directly but might put a finer point on it.

According to the specs, the Monitor Audio S8's will produce 91 dB of sound at 1 meter given 1 watt. At 60 watts the sound pressure would be about 109 dB at 1m. At 2m (6.6 ft) it should produce 105 dB. At 3m (9.9 ft) it will produce about 102 dB. This sounds barely adequate depending on your room size, seating distance, the type of music you play, and how loud you listen. Moreover, the Adcom will be maxed out. So the question is, how well does the Adcom perform near its peak power rating?

The S8 is rated to handle 175 watts. I would be tempted to borrow a higher power amplifier to see if there was an improvement.

The question should be, is there a better 60 watt amp for my speakers out there? 60 watts is plenty period. A BEL 50 watt amp will blow the speakers apart without breaking a sweat. So will many other amps with high current. Also amps under the 100 watt range will almost allways sound better than the same co's higher output amps simply because lower watt amps are easier to make with less parts(output devices) daisy chained together to get more power. If you find yourself needing more than this 60-75 watt range, something is for sure wrong with either the speaker selection or mabe you live in a barn size house.

Do you know the efficiency rating of your speakers (I'd guess in the 86-88 db range)?