there site says they have a sensativity of just 86db. That means with 1watt of power, they make 86db of noise, 1meter away. Thats a quietspeaker, not a loudspeaker. Most speakers make more noise than that
Fetch your arm bands, its about to get deep. A doubling of amp power is a 3db gain. Or, from another angle, if a speaker were to be swaped for one 3db less sensative then twice the amp power would be needed for the same volume. Getting deeper, we find 1 watt is making you 86db, so, 2 watt being double would be 89db. for 92db we would need 4 watts. for 95, 8. Then for 98, 16. 101, 32. 104, 64. Now 64watts is quite a lot. These speakers are never really going to get far past 104db. Thats on a track that will allow such power levels too.
Speakers come between 86 and 92db as a rule. Over 89db is unusual for hifi, but 89 is like doubling your amp.
check the sensativity of the speakers your interested in to narrow the choice.