Speakers 105 db, subwoofer 115db. Here is a calculator to help figure amplifier power.
It is a little basic and not accurate for small rooms but it will do for demo purposes of the differences between these speakers. 10db difference is roughly half volume subjectively.http://www.crownaudio.com/apps_htm/d...ct-pwr-req.htm
Paradigm S8 - 89db anechoic, 92db in room. Max amp power recommended 200W.
Triad Platinum - 94.5db anechoic, 97.5 db in room, 103.5 db baffle mounted. Max amp power recommended 500W.
So say your seating is 6 meters for your second row and desired level at 105 for reference.
I really like the S8s they are an excellent speaker. They measure well, have a good off axis response. Just not the right speaker for this application. You want something that is effortless when you turn it up.
I haven't tested or measured the K2s, so I can't comment.
A good HT designer will not try to just sell you something he carries. He will spec the right products for your application whether you buy from him or not. There are many characteristics of speakers and acoustic treatments to consider. How loud they can play is just one characterisitc.
Unfortunately, we have all dealt with bad salesman that are just trying to push their product on you and this makes us cautious and jaded. A good designer won't do this. It is really the right place to start. I'd look ao getting opinions on a good HT designer first and then once you know the requirements then go over equipment options.