I might be missing something here, but I thought the whole idea of these cabs was to cover a lot of ground that normally a 2x12 or 4x10 would cover? I have learnt to respect all opinions on these cabinets, and I was at one point very tempted by a BB2, but I already have enough gear. However, this is the literature (and I presume honest 'marketing' if we are to be fair to other manufacturers) on the BF site.
So, in essence, adding another Super Compact makes it equivalent to a 4x12 or 8x10? (I assume not a high end version of one of those).
If you are putting a well regarded amp into an expensive cab that is equivalent to a 2x12 or 4x10, and running out of steam...something isn't right even at 8 ohms. Either with gain/EQ or possibly the amp itself. You will also be damaging your hearing significantly if the band is competing at those volumes. I used to rehearse with a touring hardcore band and we played stupid volumes. I would constantly tell them it isn't needed, but it was all about cranking those big 4x12s. I never ran out of steam with similar amps....through standard 8 ohm 4x10s from the practice room.
To confirm, I don't think shelling out for another expensive cab is a good option. It makes no sense as that cab is to cover a much larger cabs role.
If that is the case, I would ask BF for another option, as that isn't covering what you need. Are you within the trial period?