Randy, if you wind up using just the 500, the front left corner should be used since it's "tighter", i.e. farther from a large opening, than the right corner. If you use both, the Harman paper would indicate that they should be placed mid front wall and mid back wall(exactly mid, not just almost). If you wanted to use the two and maximize output(as much as 3dB more output)rather than trying to minimize the effect of room modes, they should be co-located in the front left corner.

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Enjoy the music, not the equipment.