I recently sold a BP-17 (non cubed).
I thought it was very sterile sounding. To my ears the midrange was "thin". There simply was not enough "body" to the music. Clear and transparent - yes. Not bright per se. The music simply was not at all engaging. I could never listen to it long.
My other preamps are a Prima Luna Dialogue Premium, an Eastern Electric MiniMax pre, an old aragon, an old acurus LS-11 and a Music Fidelity A3CR.
I like the Music Fidelity the best. Speakers are older B & W 803D’s
Overall the Bryston was "transparent" but I did not like the perceived freq response - it just did not sound "right". It was very obvious every time I inserted it into the system. I wanted to like it as well but would remove it after a few songs. Hard to describe what I am trying to relate. Perhaps overly "thin" sounding is best with a recessed midrange. It was "thinner" than the old aragon, the LS-11 Acurus or the Music Fidelity. The A3CR is great and was a highly rated Pre (Stereophile) in its day. Dual mono etc, very heavy.
I am getting away from tube Pre’s. The Prima Luna is not at all thick sounding but does not have the resolution of a good solid state preamp. I very much like resolution but the Bryston simply sounded "wrong" and to my ears it was always very obvious every time I inserted it (at least that model - I bought it used sight unseen and had never heard one prior). I am certain it has a ruler flat freq response when measured but nonetheless it sounded disjointed and not at all "musical" - altho this sounds "corny" there was no emotion to the music - I always wanted to remove it quickly and replace it with another Pre. My amps are an NAD C-298 (very nice), a very old Aragon 2004 and a Quad Artera. The bryston did not play with any of them well - always the same "nonmusical/flat" sound.
Hope that helps. I am not dogging Bryston - they make bullet proof stuff. I hear their latest stuff is somewhat warmer sounding.
To each their own I guess. The person that bought the BP-17 from me was glad to find one (he was going to use it in a hunting cabin in northern wisconsin - a true audiophile if there ever was one!)