Here's a possibly confusing way to find good places for both your head and your speakers -
http://www.johnlsayers.com/phpBB2/viewtopic.php?p=18059
with your splayed walls, it will be less definite but should still work if you use the actual room dimensions
at the speaker location when deciding where to locate the speakers; then, use actual room dimensions
at your head when deciding that position -
I'm just now getting into ETF software, I got the entire package with calibrated mic and extra plugins; I've already noticed that things don't always remain predictable (sorta suspected that

) - but ideally, using something like ETF to check flatness of each speaker at the mix position would be a more guaranteed way of getting things balanced out modally, especially in a splayed room...
I'd start with your speaker's woofer centers about 26" from each side wall (this would put distance from your head to each speaker at 68" for an equilateral triangle), and pull them forward enough to put the dome in the center of the woofer at 33-34" away from the front wall - there should be nulls at 21", 27", and 42" from the front wall (assuming your front-back distance is still 14 feet) so positioning relative to front wall will probably be pretty picky. those three harmonics are at 161 hZ, 121 hZ, and 81 hZ, so if you have a way to monitor at the mix position with any kind of spectrum analyzer plugin, those would be the frequencies to try and balance out by moving the speakers forward or back; again, there's only 6" difference between two of the nulls, so it will be tricky.
These measurements (woofer centers at 26" from sides, and 33-34" from front) would put your head at about 91-92" from the front wall for an equilateral triangle - this isn't cast in stone or anything, just a good place to start. You don't want your head centered front to back; there's another null there, at 40 hZ; getting stuck there would make you think your woofers were blown

; keep in mind that moving anything as little as an inch or two will change the results; you may not hear them as such, but I sure can SEE them using ETF in an ordinary (crappy) room - in fact, results change VERY noticeably at lower frequencies I was testing depending on where I was standing at the time - anybody wanna rent me for a bass trap ?
Then, there's the
vertical dimension - about 6" away from dead center for the woofer would be a good starting point on that.
Most of what I'm doing to get this info can be found at the above link, BTW... Steve