Speaker Sensitivity AND Power Requirements

how big is the man cave
what and how loud do you listen ?
what speakers are you using now ?

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.