What does moving from a 150 watt amp to a 400 watt amp get you?

I would make several points:

1)As a practical matter what you are using with this particular speaker is a 240 watt amp, not a 150 watt amp. The amp is rated at 150 watts into 8 ohms and 300 watts into 4 ohms. The impedance curve of the speaker, as shown in Stereophile’s review, indicates an impedance averaging about 5 ohms across almost all of the frequency range below 1 kHz, which is the part of the spectrum that encompasses most of the energy of music music. It can be calculated from the 150 watt/300 watt 8 ohm/4 ohm numbers that the amp is capable of 240 watts into 5 ohms.

2)The difference between 400 watts and 240 watts is about 2.2 db, which while not quite negligible is not much of a difference.

3)IMO design differences between amplifiers are likely to be vastly more significant from a sonic standpoint than a 2.2 db difference in maximum power capability.

4)Everything else being equal more amplifier watts = more amplifier $. IMO it is usually desirable to have as high a percentage as possible of the dollars one chooses to invest in an amplifier go toward quality rather than toward watts, assuming the number of watts is sufficient to avoid getting near the amp’s clipping point.

Good luck. Regards,
-- Al

Correction to my previous post:  In the first paragraph "music music" should have been "most music," of course.

Regards,
-- Al
 

Well, I agree with most of what has been said.  Normally the advantage of adding power, isn't necessarily adding power itself, but having the power supply with larger current capability. Power supplies don't have to be regulated, but a good regulated power supply along with good current capability normally provide a amp that is dynamic and full... of course a poor design can kill that whole theory.  Overall, your Ayre is a nice piece of equipment.

Omg this topic again. More watts doesn’t mean better sound quality it just means you can play your music louder. You will never use 450 watts unless you listen at an ungodly volume and you have a very, very large listening room. The fact is most people use about 8-15 pure watts when listening to music. Focus on the sensitivity of your speakers before spending ridiculous amounts of $$$ on a amplifier based on how many wpc it has. 

Cheers

A big amplifier is useful for a clean sound on dynamic peaks as in symphonic music. Harbeth's Alan Shaw recently did a demonstration of his big M40.1 speakers and the digital power meters on the monoblocks that he was using indicated they were delivering more than 500 watts/ch on peaks.
Fortunately beefy pro audio amplifiers do not cost mega bucks, and can be very good for home audio. See here for a serious test (with an AP audio analyzer) that makes precisely this point: http://www.homecinema-fr.com/forum/amplificateurs-de-puissance-haute-fidelite/mesures-ampli-yamaha-p...