Power conditioners

Take a look at PS Audio's Duet or Quintet products.
Here's a good read from their website: http://www.psaudio.com/products/quintetmoreinfo.asp.

Is there a reason why power conditioners should not be used with a power amp?

Yes...power amps need to store and draw on high instantaneous power (big capicitors and big power supply).....therefore any device that may "choke" power could affect the dynamic headroom. Think of a river flowing to fill up a dam at a power station....normally the dam has enough energy stored behind the dam to handle things. Also a big dam is very very expensive just like a power amp power supply. Therefore manufacturers will skimp on the power supply to reach a price point (this may not influence the amp performance until the amp is driven hard or with a difficult load). So when the system is really pushed it may help if the "river" flows unrestricted into the dam (especially true if the power supply is modest).

Thanks for the explanation and "illustration" Shadorne!

Shadorne, That's a dam good analogy :-)

I have experienced 50 wpc amps sounding more powerful than some 200 wpc ones on my Maggie 3.6's no doubt due to their nice power supply.