Room Acoustics Problem?

I'm assuming your measurement were at the listening position, if true, then your system measures quite well. The 4-6 dB spikes in the upper midrange could be sonically objectionable, but they could simply be measurement artifacts. Playing with toe-in might eliminate them. You might also consider one of the DSP room correction products from Perpetual Tech, TACT or Sigtech.

A piece of carpet in the hardwood floor will help to improve sound.....

While I agree with the previous two folks, I also think that the combination of Bryston and Thiel can sound bright and forward under some conditions. If this system does sound "bright" to you, DO NOT toe the speakers in unless they are wider apart than their distance from your listening seat -- keep then parallel to each other. Also, this system can be VERY cable-sensitive. What speaker cable are you using?

Best of luck,
Joe

OZfly, I assume that you already have corrected for the ERROR added by the measuring device. If not here are the corrections. ADD the error value to measured value and review the results to see where the problem is.
Freq error
20 6.2
25 4.4
31.5 3
40 2
50 1.3
63 0.8
80 0.5
100 0.3
125 0.2
160 0.1
200 0
250 0
315 0
400 0
500 0
630 0
800 0
1000 0
1250 0
1600 0.1
2000 0.2
2500 0.3
3150 0.5
4000 0.8
5000 1.3
6300 2
8000 3
10000 4.4
12500 6.2
16000 8.5
20000 11.2

Of course this may make your upper mid-range, low treble problem worse. In that case room acaustics would not cause big boost unless you have highly reflective surface-mirror, cabinet glass or big picture frame between you and speakers. If not, thiels are known to on brightet side in low treble range. Joe suggestion in combination with near field listening, verified by trial and error re-measurements should do the trick or try different IC between Pre amp and amp.

Thanks all. I did measure at listening position and did adjust the readings to correct for instrument design. Speakers are fairly parallel to one another and I do have an oriental on the floor. But, I used a slightly different adjustment than Nilthepill recommends (with those adjustments, things look better -- there is still a big dip in the 32-50 Hz range and a 2-4 db spike at the 5k - 6.3k range but the 20k is only down by 5db -- everything else is in the 2db range with a couple of 3db issues). I am using the Stealth Premier speaker cable but agree that an alternative might be good. The low end dips and upper mid spikes still drive me nuts when I'm listening so please keep the suggestions coming. Thanks.