I have played a few SR5s and owned a Bongo5, and virutally all EBMM 5-string basses I've played have had a good low B. Here are a few helpful hints. Some people adjust their saddles to follow the natural radius of the fretboard, thus the A & D strings are higher than the E & G. I actually do this as well, but I raise the B string saddle up higher than the E string saddle, at least to the same height as the A string. Because the B string is so thick, it needs more room to vibrate in order to ring out clearly. Raising the saddle and lowering the pickup a bit on the bass side should help quite a bit.
Aside from that, try using a string with a hexagonal core, not a round core. Strings with a round core have less tension, generally speaking, which can result in a "floppy" feeling string. The hex core strings I've used have more string tension, so they have more focus and a stronger fundamental, especially on the lower strings. I prefer DR Lo-Riders, but any string with a hexagonal core should help the situation.
Hope this helps. Sometimes you get a lemon, but almost any bass can get a good low B with a little tweaking IME.
Aside from that, try using a string with a hexagonal core, not a round core. Strings with a round core have less tension, generally speaking, which can result in a "floppy" feeling string. The hex core strings I've used have more string tension, so they have more focus and a stronger fundamental, especially on the lower strings. I prefer DR Lo-Riders, but any string with a hexagonal core should help the situation.
Hope this helps. Sometimes you get a lemon, but almost any bass can get a good low B with a little tweaking IME.