I generally agree with the comments above, but let's take the answer a step further. If the problem proves NOT to be the recording, then I'd say the speaker is the culprit. I doubt very much that either the preamp or the power amp is the cause of the problem.
Bear in mind that massed brass generates a lot of acoustic energy in the upper mid-range, not just the high frequencies. So, you have be experiencing a limitation caused by the B&W 805's. I have sold B&W speakers professionally, and their lower-priced models can be a little edgy in the frequency range you are describing. Try borrowing a set of speakers that are known to have smooth upper-mid and high frequencies and see how the system sounds.
The last item you may want to explore are your interconnects. You don't state which model of AQ interconnects you are using, but if they are among the lower priced models that AQ makes, you might want to try a different brand, such as Kimber's Hero, or Alhpa-Core Goertz TQ2. I have found these two interconnects to do a very nice job in my own system with the upper frequencies.
Bear in mind that massed brass generates a lot of acoustic energy in the upper mid-range, not just the high frequencies. So, you have be experiencing a limitation caused by the B&W 805's. I have sold B&W speakers professionally, and their lower-priced models can be a little edgy in the frequency range you are describing. Try borrowing a set of speakers that are known to have smooth upper-mid and high frequencies and see how the system sounds.
The last item you may want to explore are your interconnects. You don't state which model of AQ interconnects you are using, but if they are among the lower priced models that AQ makes, you might want to try a different brand, such as Kimber's Hero, or Alhpa-Core Goertz TQ2. I have found these two interconnects to do a very nice job in my own system with the upper frequencies.