Speaker Sensitivity AND Power Requirements

It has been many, many years since I've sold Audio,  but I always asked 3 questions,  which tomic601 touched on... 
How loud do you listen?, How big is your room? and what kind of music do you listen to? 
If your room is not too large and you are a chamber music listener or small jazz ensembles, then yes, You will squeak by, but if you are a rocker or like big orchestral pieces,  it won't cut it.  6 ohm impedance on these speakers, so most amps will drive them well,  but I'd look at more power.... If you have a beefy high current amp, 40 to 50 watts will push them, but if you are staying with a receiver, I'd look at 60+....  
I hope this helps, Tim

This might be helpful.  It's not limited to home theater.

http://myhometheater.homestead.com/splcalculator.html

It is a good question.  I have a pair of 90 dB sen speakers in my workshop which is 16 × 20 and it plays to pretty decent volume with a 15 watt receiver but the system runs out of steam fast.

i agree with timlub--i'd look for more power--

Hi again all, thanks for all the good responses. Here are the answers to questions asked.  My man cave is actually pretty big, it's a basement of sorts and is just over a 1,000 square feet.  My gear is a few feet out from one of the long walls and my work table is about six and a half to seven feet from my speakers. These are older Yamaha stand mounters. NS-A 915 YS. They say they need a minimum of 10 watts and can handle up to 120.  I play music while I'm working on my hobbies, It's background music and not dedicated listening as in my main system but I still want the best sound possible. I know everyone here gets that. 
My main taste is heavy rock, Scorpions,Zeppelin, Sabbath, The Who, UFO, etc.  I also love the softer side of rock too, Elton John, etc. Blues, old school jazz, oldies and some classical round out my likes. My cd player in the cave system is a 5 disc changer Yamaha.  This current set up plays nice and it easily gets loud enough as most of the floor is cement.  I did put a throw rug between my table and the system. I was mainly looking at the Wharfedales due to the fact that they are so heavily discounted and I like the sound of my floor standing Wharfedales in my main system.  More comments are appreciated.