Matchstikman, I like your diagonal configuration. You might try shifting your speaker-listener-speaker triangle a little bit so that you're not lined up perfectly on the diagonal.
I'm an advocate of using multiple asymmetrically-placed subs to smooth out the in-room bass, a technique I learned from Earl Geddes. Small rooms are especially prone to lumpy bass because the room-induced peaks-and-dips tend to be larger and spaced farther apart in a small room, which makes them more audible. Multiple dissimilar peak-and-dip patterns at the listening position can help smooth things out, which allows you to turn up the subs a bit higher (giving a more natural tonal balance) because you don't have strong bass peaks that boom, forcing you to keep the subs turned down low. Whether you use a symmetrical or asymmetrical setup, two subs will be better than one if you choose wisely.
You see, another issue in many small rooms is excess boundary reinforcement because the room boundaries are all pretty close to the sub(s). So you don't want subs that are "flat" anechoic; rather, you want subs that would roll off gently under anechoic conditions - which the room gain will offset. I'm not sure what would be ideal in a 10 by 10 room, but the 6 dB per octave rolloff of a low-Q sealed box would probably be a good starting point.
Finally, if you're going to place any of the subs well away from the main speakers, you want to make sure those subs aren't contributing any audible lower midrange energy. If they are closer to your ears than the main speakers, you could hear them as separate sound sources if that lower midrange energy is loud enough. So a steep-slope (24 dB per octave) low-pass filter is desirable.
Duke
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