BHK 250 definitely sounds better with the BHK Pre.
I'd spent over a year listening to the BHK250 at the factory I worked at,
and
I actually think it sounds good, certainly not a turkey.
Because they are big turkeys!!!!!- ebm
And to make it not sound good, you'd have to do a lot wrong.
I currently own a Datasat RA2400 (I managed to get it cheaper than a used BHK 250), and I'd like a BHK Pre when I can afford one, and I get spousal approval on such a purchase.
If you're asking because you want an idea of what they sound like, I find them to deliver a clean detailed sound, with a good punch in the bass. Of course the loudspeakers have a very significant role in the final sound. I found the BHK 250 quite a good performer, though we'd had better tested in the system.
A surprising amplifier was the Prima Luna Dialogue Premium HP that had resistors and capacitors in the signal path upgraded, and Prima Luna KT120's.