Basic question about impedance and watts


I just bought a pair of Thiel cs3.5's and am now looking for an amp. If the impedance is 4Ohms (i think this is the correct value, i didn't get the owners manual) and the recommended power is 50-150 watts (once again, a guess), how much power should the amp have? Do i need an amp that is 50-150 watts at 8ohms, or do i need an amp that is 25-75 watts at 8Ohms (assuming the amps watts double as the impedance halves)?
I guess the reason i had no luck searching for this is because its so basic.
if anyone knows the specs for these speakers, could you let me know? the owners manuals are available on Thiel's website for most, if not all, models except the 3.5s.
ketchup
I've found Aragon's customer service to be as good as Thiel's. Also, the laid back sound should take the "bite" off of the thiels nicely.
With all due respect to Elevick, I believe that Mondial the parent company for Aragon has recently been bought by Harmon. Judging by the previous comments posted here on Audiogon, I think it's fair to say that Harmon's reputation for customer service has been less than sterling. While Harmon may make a special case with these higher-end products, only time will tell and I think that untill further notice there may be more risk to owning Mondial products than previous owners may be accustomed to.
Sorry Unsound...Mondial Designs was purchased by Klipsch, not Harmon. How that has affected their customer service is a question I cannot answer.
Goinbroke, thanks for the correction. That might be better than being under the Harmon umbrella.