How important is S/N Ratio....?

There is no "standard" dB level for a jet plane. Some business jets are so quiet that we don't know they have arrived at our little local airport until they taxi up to the terminal. On the other hand, I have had occasion to work with an F15 fighter in a flight testing project. Let me tell you, a full afterburner takeoff from a couple of hundred feet beside the runway is an awesome experience. We were required to wear ear plugs, but even so it was loud. I believe that even one unprotected event would do damage.

Wavetrader - that's good!

Clio09 - more headroom is always better if you can afford it. If you have let say $1k to buy an amp would you be better with mediocre 1kW amp or great 100W amp. 1kW amp should be twice louder but not always. Amps are rated for nominal power and 100W amp might have very large peak power being designed by good conservative company. 1kW amp that cost the same as 100W one will have most likely worse parts since power supply, case and heatsinks have to be 10x larger and something has to make-up for their cost.

Much worse if you choose SS amp over tube amp that you like only because of 200W over 100W (and 200W tube is too expensive). Another example might be selling 50W class A amp to get 100W class AB amp etc. There is a very little difference in sound level between 100W and 200W.

You guys are funny....jet plane takeoffs...

Eldaford - Jet plane was a joke but I think you mixing landing and taking off. During landing they are very quiet.

I read once that 120dB was equivalent to standing next to jet engine during take-off (should I say running very fast). To visualize what 120dB level is try to imagine large GE Jet engine at full power in front of your door (neighbors might not care too much for it).

Keep in mind I didn't start the Jet takeoff thing.
I lived near El Toro MCAS and heard F-4 takeoffs which even with them being as easy as possible...no afterburners or aggressive climbouts, you could hear them for several minutes echoing thru the canyons. I was at an airshow and witnessed a flyby of a Concord! Man, that thing was LOUD.

This whole thing needs to be thought thru more thoroughly.
How quiet is your room? 40db at 0-dark-30? Let's say you can play it pretty much as loud as you'd like...not likely but we can dream! Subtract 40 from 120 and you've got 80db range. This is more than Vinyl is capable of and stretches the practical (NOTE: practical, not measureable) CD limits.

Sorry, this is a non-starter and a fine example of wishful thinking and specsmanship taking over!

There are great numbers of Credible Systems which use hi sensitivity speakers coupled to low power amps. These systems en toto draw less than my bedside reading lamp.