Attn: Audiophiles need help with tower speakers

[mseller]

I got the JL Audio MHD600/4 powering 4 JL Audio M770-TCS Tower speakers. I know the amp puts out up to 150w per channel and the speakers are rated for 100w RMS so I want to make sure I set the input so it doesn't blow the speakers. I got the amp set on 12db HP filter @ 100hz. I put a 170hz sine wave on my ipod to test the output voltage of the channels. The manual says that I want to measure 24.5V. Now if I want 100w output per channel I am assuming I need to measure 20V cause(correct me if i'm wrong) v=I*R and since speakers are 4 ohm then current would be 5 amps. And then P=V*I so power would 100W. However after all that I am only measuring about 5V per channel. I was scared to turn up the input more cause I didn't know if i was doing it right and didnt want to blow anything. I turned it all the way up for a brief moment and only got about 9V. Re-reading the manual I see that I should have played a 1khz sine wave and I shouldn't have had the speakers connected. Will have to wait till next weekend to get back to the lake to re-measure. But does anyone see anything else wrong with my logic?