I happily ran the BHK pre for 3 years along with the 300 mono's. I think it's a great preamp for the money, and I really liked the tube rolling flexibility for system tuning.
But I am an itchy audiofool, too, and my budget has recently increased (kids all through college! house paid off!) so I tried out the Luxman C900u pre and it plainly revealed to me how much more informative a preamp could be, but obviously at a higher price in this case. Once I heard that much more musical info, I didn't want to go back, even though the Luxman C900u proved to be too "neutral" for my system and tastes (I run TAD CR-1's that need to be pulled back a bit from getting too hot).
Next up was an ARC Ref 40 tubed pre, and it is still riding well in my system. It has all that musical information, but with a bit more harmonic fleshing out, which is hitting my system really well right now.
So, if you are willing to spend more money, there's more to be had, but it's no "revolution", "wipes the floor with it" kind of thing. The BHK gear is the real deal, IME/IMO, delivering a really good musical experience. I could have happily lived with them both for years if my budget hadn't expanded.