what receiver to choose ?

[Kurt04]

I have rechecked technical specs of these models and what i discovered was that in surround mode Kenwood has 5x50W, Yamaha 5x60W and Sony is 5x80W
Now, i have 80W sub and I want to get good floor speakers (at least 100W). and most of "entry-level" receivers today are at least 100W in surround

I am very confused because many people say the real (or so called effecient) power specs are 50% lower that manufacturer says, if so how to check the REAL power output?
If i never listen to loud music and volume is usually at 20-30% would i ever need the whole 80W? Can you explain that please or give a good link for this info
And if in surround mode receiver gives 5x80W it would give the same power per channel in stereo, as far as i understand.

Also is this correct that if i'll listen to music using 5.1 receiver the quality would be way lower than with stereo amp ?? or the stereo would only give me more power (that I probably don't need). I mean what is wrong with using 5.1 receiver just to listen to music?
Also i have seen not a big price difference between stereo and 5.1 amps from same manufacturers, so why to go for less from the start ?
unfortunately all the great hi-fi amps you have mentioned are not available at stores and i dont want to order from the internet.

Thanks for helping!!

p.s. my old good shelf speakers are 6 Ohm how receiver can affect them if it works in 8 Ohm mode.