Power supply VA rating and how much is really needed


I have a general question. Two actually.

How much capacity of a power supply is needed to allow for each channel in a multi channel amplifier feeding demanding speakers preferred? 

Is 300VA-400VA per channel enough?  Will less be detrimental to performance and SQ? Is more always better?

What are ideal specs for a multichannel ( or stereo amplifier ) that will provide a pleasant experience.  Not looking for the 'best' of the best... but for a decent amp... what are specs that I should be focused upon?

I realize SQ is important, but specs play a role in narrowing down the list I have put together.
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Second question:

How much output current capacity is need/required/preferred to drive speakers adequately?  And how to calculate the output if the spec isn't given.  I tried google, sadly I didn't find the formula I was looking for.

Is for example 40A enough? Is 30A?  

What factors need I consider in figuring out what spec matters most?

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My speakers consist of B&W CDM 9NTs with matching center channel.  

Contenders:

Emotiva XPS 5ch
Monoprice 5-7ch 
Rotel RMB1585
Odyssey Stratos 2ch and adding emotiva basX 5-7ch or something like it ... possibly used market parasound, rotel, acurus, etc for surround duties.


Not sure which of these actually have the best specs that translates in to best bang for the buck purchase to provide sweet midrange, tight punchy controlled bass, and nice sweet highs but not to bright.

I know the Rotel is highly recommended based on blending well with my speakers - but when do specs trump sound? Or does it?

I am removing power cords, fuses etc from the equation for a moment.

lightfighter2018
Sorry, I've been on somewhat of a hiatas from some frustrating audio testing and then thanksgiving and then getting sick. 


Generally speaking, I would not pay too much attention to how many amps output.  The specifications that say "40A output" are pretty meaningless.  The "output watts" is a specification that will indicate the overall size of the power supply.  A 500 watt monoblock amp is going to have a rather large transformer and a large power supply capacitor bank.  Obviously, you are not going to use all 500 watts for a single speaker, but the benefit is going to be much smoother sound, fuller midrange, and much stronger and fuller bass.  It also depends on how hard your speakers are to drive.  A smaller 150 watt amp would probably be fine on a more efficient high impedance speaker - such as a flat 8 ohm speaker that is 91db efficient.  Once you start going down in impedance and efficiency, you really want a beefier power supply - which translates to a larger power amp.

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Another part is the sonic signature - do you want a very fast responding "Class B" type of amp, or do you want a very warm sounding "Class A" type - or something "neutral" in the middle.  It all comes down to personal taste.  I just finished my own evaluation of different amps and have heard a whole lot of different electronics when I went to RMAF.  In my testing, I would say that the Parasound was the best in fullness and natural sound, but it was too warm for my tastes.  Bryston cubed amps were very nice and very high resolution, but were too thin/fast for me (they are just about the closest to a Class B amp you can get).  The Classe Audio monoblocks I tested sounded very clinical and sterile in my system, but they did have good resolution. 

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So, in my frustration, I just went back to Emotiva and purchased a pair of their 2-channel fully differential amps (the XPA-DR2 models).  I have one amp powering the front left / surround left.  And the second powering the front right / surround right.  Obviously, I'm balancing the power supplies in the amps so that they are used most efficiently, but at a rating of 550 watts per channel, it is totally fine.  I will say that after hearing gobs of ultra expensive electronics and a variety of different sonic signature, the new Emotiva differential amps are PRETTY DAMN GOOD!  I originally had Emotiva XPR-1 amps (1000 watt monoblocks) for my left/right which I sold earlier this year and regret that.  The new amps are only 4 days old and still burning in so I won't have a final judgment for another week or so.  It's very difficult to tell if these are going to be better than my original XPR-1 amps or not.  I will say my system sounds the best with Emotiva monoblocks (whether they are the old XPR-1 or the new XPA-DR2).  The Emotiva are very neutral amps, but they have excellent resolution.  The sounds/vocals are very realistic and they are extremely engaging with my B&W D3 speakers (which none of the other amps really gave me).  At this point, the amps do not quite have the amount of bass/midbass that I would like, but they are still burning in.  They are a slightly different amp board and the power supply is the switching power supply instead of a massive transformer and capacitor bank.  That may translate into how much bass strength I have.  I will know more in about 4-5 days.
I will agree with Eric's statements that Emotiva preamps / processors / DACs are not that great.  They are rather dull sounding and "closed in" sounding with lack of resolution, separation of instruments, and depth.  Their amps have always been very excellent, however.