Go to Whaferdale's website, and take a look at the specs for these speakers. Are they 4 ohm or 8 ohm? What is the rated sensitivity?
For 4 ohm speakers, I would feel safer about driving them with an external amp. Most receivers usually can't power 4 ohm speakers properly. Even if you do get good volume from your receiver driving 4 ohm speakers, the sound is usually a bit lean, that's because the current is not there to drive those 4 ohm loads. A beefier external amp will give you a "fatter" sound.