Something definitely sounds off with that particular unit's performance, and I suppose it could just be worn out tubes or poor tube choice. I ran one for ~3 years with much satisfaction. It replaced a VAC Ren Sig II convincingly in my system, and I only moved on for an AR Ref 40, which does offer more, but doesn't exactly embarrass the BHK pre. I found soundstage depth and bass to be strengths of the preamp, not weaknesses.
Trying a new set of tubes is a good place to start. Check out the PS Audio website forum for some detailed discussion threads about the many varieties that are possible, with a nice number of sonic impressions reported. After comparing 10 different varieties, I was smitten with Amperex 7308's in the unit, because it offered the right balance of fullness in mid-bass through low mids that my system needs, while not sacrificing the highs.
Since you have a used unit, I'm assuming it is well broken in. Several have reported some big changes in their first 100 hours (wasn't a big event for me when I broke in a new one).
