What you want for your sub is this.http://www.rivesaudio.com/software/TestCD.html
This cd has test tracks that are corrected for the radio shack slp meter. So it is accurate below 100 Hz unlike the other suggestions. Track 32 to 40 are the important ones to find the best location for your sub. Those tracks have the corrected 20, 25, 31.5, 40, 50 63 80 100 and 125 Hz test tones. So here is what you do: Set your sub crossover to bypass and your receiver crossover to 80 Hz. Find the 3 or 4 different locations that you want to put the sub and run the tone tests with the rives cd from tracks 32 to 40. You want to run the test tones with the phase at 0 and then 180 degrees in each location. Keep a chart of all of this information. The best location and phase will be the one with the flattest frequency response. Since you are getting full range speakers (m60's or m80's) you could also test each location and phase with different crossovers for the front speakers as well, but only if your receiver allows for the mains to be crossed differently that the center and surrounds. For example in the first location run the test tones with 40Hz, 50Hz, 60Hz, 70Hz and 80Hz each with 0 and 180 deg on the phase setting. So that is a total of 10 runs that you have recorded in your chart for the first location. Repeat this with each possible sub location and pick out which location has the flattest frequency response in your range.
For my room I ran the tone tests for about 3 or 4 locations and it turned out that 80Hz worked out best for the crossover with my m22's. I tried 60 and 70Hz as well but the frequency response was a huge mess. The phase makes a huge difference when trying to match your mains to the sub. In one phase setting my frequency response was +/- 8 dB from 25 Hz to 160 Hz and with the other phase setting it is +/- 2dB. That is what my in room response is right now. You can't get much better that than since the tolerance on the Outlaw sub is only +/- 2dB. So all this work is definitely worth the effort.