I finally have a gig report on my "PBX" -- a BX-500 in a PB-200 cab with the old tweeter and L-pad but a new 15" 4ohm Neo speaker, creating a 500W combo in a 42-lb package. (Looks pretty much like bass4worship's above except with a black tweeter.) Nice thought, but...
My original basement findings on the new combo -- that the speaker doesn't seem to care all that much for its confines -- were borne out at volume. In a classic rock band (Aerosmith, Zeppelin, Nugent, Steppenwolf, and the like -- read, "bottom") I had to boost the bass all the way to 4:00 and cut both mid bands (at 300 HZ and 900 Hz) rather severely to get the combo to sound sort of like a bass amp. It was plenty loud, but still with that low-mid crowdedness that annoys the guitar player and doesn't really go "boom" like a real bass amp should. Didn't leave much room for tone tweaking after that.
To be fair, I will probably take it to the next gig and run the BX through my regular cab -- an old Sonic Micromini 115 with a KappaLite 3015 in it. This won't be until the end of the month, so I'll just have to wait...
That having been said, it will be lovely for my soft-jazz group that doesn't require a ton of volume and likes a lighter tone, so I'll be able to use more of the abundant mids. It will also suit the acoustic-rock band with a conga player as I won't need to go quite so deep.
One of the few things I don't appreciate about this otherwise fairly adorable head is that the direct out is pre-EQ -- meaning I have next to no say into what goes to FOH. I use lots of effects and I take solos and change my tone frequently through a gig, and not to have given me any boost or tone manipulation is kind of... well, mean (to my view). That design decision relegates all of this fabulous tone-shaping capability to a mere stage monitor.
Be sure to take this review more as a critique of my combo design skills than as a strike against the BX-500. Once I get it through my "real" cab, then we'll talk turkey about the BX-500 itself.