I own K9's--at one point I had three pair, but sold two pair to make room to diversify my "stable", but still have a pair. I ran all of them in "extended" mode. All "normal" mode does is add a 1 ohm resistor to the woofer circuit and kills the bass response, reducing the performance of the speaker, but slightly lightening the load on the amp(s). As for amps, I initially used a pair of Aragon 4004's--one for the mid/highs and one for the woofers, and they performed flawlessly (didn't even really get hot), and I drove them hard. Now they are powered with four Krell KMA 160 monoblocks. The Aragons are often referred to as "baby Krells" or "poor man's Krells" because they were primarily designed and spec'd by Dan D'Agostino of Krell fame. There are two impedance dips below 1 ohm--one at about 33-35Hz and a second at ~7KHz, hence the reputation as "amp killers". They certainly like their "juice". It is not all about total power rating, but rather the ability of the amp to supply enough current to maintain voltage into low impedance loads. My Krells are only rated at 160w each @ 8 ohms, but "double down" to 1280w each @ 1 ohm (as per the factory manual). The Aragons are very similar in this respect. Hope this helps! ENJOY--they are fantastic speakers.