Subwoofer calibration quandary...

Thanks for the response. :)
Here's what I have so far according to my RS meter and Test CD.
Listening (measurement) position is at 3/5ths of both room dimensions.
First-order modes are 25 and 33hz.
The sound of the curve shown is basically weightless in the upperbass, while dinosaur foot-stomps dislodge knick-knacks.
Bass instruments have the requisite grunt, but not much personality.
I can iron out most of the upperbass valleys, but the low and mid bass end up at +9db.

db - hz - (deviation from 1khz reference; db)
73 - 20 - (-2)
74 - 25 - (-1)
74 - 31 - (-1)
74 - 40 - (-1)
77 - 50 - (+2)
76 - 63 - (+1)
66 - 80 - (-9)
72 - 100 - (-3)
64 - 125 - (-11)
71 - 160 - (-4)
72 - 200 - (-3)

The sub is a Paradigm Servo-15 placed against the center of the 22' front wall, 3' behind the main speakers.
The mains are B&W CDM 9NT crossed over at 80hz @ 60º Phase.

I'm currently using a 35hz crossover @ 30º Phase, and the results are slightly better if I can accept the slight reduction in 20hz extension.
The new phase angle seems to partially mitigate the 50-60hz hump and 80hz null. (the hump begins to reappear if the level is raised much further though)

BTW, if I have one nit to pick with the Servo-15, it's that it's frequency range is too broad. A steeper crossover filter at 35hz would be nice for integrating with large speakers. The bass is extremely clean and effortless at high SPL though.

50z crossover @ 30º:
db - hz - (deviation from 1khz reference; db)
69 - 20 - (-6)
72 - 25 - (-3)
74 - 31 - (-1)
75 - 40 - (0)
74 - 50 - (-1)
74 - 63 - (-1)
71 - 80 - (-4)
76 - 100 - (+1)
67 - 125 - (-8)
72 - 160 - (-3)
73 - 200 - (-2)

The 125hz valley is purely the main speakers and listening position within the room. (the response from 63hz - 200hz is the same with or without the sub)

If I move toward the center of the room, the null shifts downward to 60hz, basically gutting the midbass and causing a large rise between 20 and 40hz.
20hz extension is no problem at all for the sub, though I often wonder how much impact it actually has on the quality of the bass response.

I can use a 120hz crossover, allowing the sub to fill in the 125hz valley, but this results in a shelved response, with the range from 20-60hz being 9db higher in level than the upper bass, and 7db higher than the reference level.
Tends to vibrate the light fixtures and windows audibly.
The 8'x5' living room window sounds like it's gonna collapse at high levels, and the character of bass instruments is not particularly realistic.

Flrnlamb,

Thanks for the detailed response!
The room is 13x17 with an 8' opening into a 10x10 dining room at the speaker end.
Here's a link to an edited illustration I made a few years ago for the tilesetter.
(white areas are walls; tiled area is floor)
http://www.byrographics.com/media/room-setup.jpg

Thanks.
The figures posted already have these corrections.