Well, although the topic is answered I'll chime in with my musical money wrench anyway... I don't personally like the sound of the low B strings, I don't think it's an amplification problem as much as the actual string itself sounding toneless and dead. If you watch five-string bassists carefully - really carefully - you'll see that they agree, because they play way less than 10% of their notes on 1/5 of their strings. It's a mere thumbrest, as so many of them joke. Maybe a 40" scale would help, there are builders who have gone to 36" but of course, most strings don't fit.
There certainly are musical reasons to wish that the low B strings did work better, but I'd personally rather not play bad-sounding notes. :sad1: I built a five-string and went the opposite way - EADG&high C, just because I wanted them all to sound good. Again, watch how often five and six stringers actually play that sucker.