Do not go by PMPO (peak mean power output), it is a mis-leading unit. Go by RMS (root mean square) wattage.
Check the frequency range. Good range is 20KHz to 40KHz.
You can't really go by specs. but you have to experience the sound quality. Go to a multibrand showroom, such as Chroma, Reliance Digital, so Unibrand outlets and experience Hometheatre systems of various makes before making a buying choice.
A THX certified HTS would be a good one.