The recommended load impedance is over 1000 ohms according to what you wrote. So just play around with the settings on your Phonomena when it arrives. Per the Phonomena's specs I found, you have several load setting so I suggest you play around with the 660, 1000, and 2000 settings first, but by all means try as many out as you'd like. In my experience, the higher the impedance, the more open the highs become but the bass becomes looser and vice versa.
I don't believe the impedance setting you choose will have any noticeable bearing on the volume. You need to adjust the gain to increase/decrease the overall volume. The Phonomena has several gain settings which should work well with the 20XH. I don't know about the settings in your BK preamp. Maybe there's a way to adjust the gain in the BK. Good luck.
I don't believe the impedance setting you choose will have any noticeable bearing on the volume. You need to adjust the gain to increase/decrease the overall volume. The Phonomena has several gain settings which should work well with the 20XH. I don't know about the settings in your BK preamp. Maybe there's a way to adjust the gain in the BK. Good luck.