What would give more volume--two combos with A/B box or convert one combo to a cab?

[skabalka]

My band has a couple of upcoming shows, and one venue will not have PA support for my bass amp. It is a fairly small venue, but my Ampeg BA210SP simply won't be loud enough on its own -- it is barely loud enough for practice. I found a Peavey Combo 300 on Craigslist that is much louder, so now I have two combos. My question is what is the best way to use these for a live show?

I have an A/B box so I can run my bass through both combos. I could also remove the Ampeg amp and use the Ampeg 2x10 as an extension cabinet for the Peavey Combo 300. I don't have the cash for another cabinet, though, so I am limited to using what I have.

Which option would be louder or work better? Any suggestions would be greatly appreciated.

Here are the specs:

Bass: Ibanez SRX690

Amp 1: Ampeg BA210SP, 2x10 + horn, 220 watts, no line out, no effects loop, no power amp in or pre-amp out, no speaker out for an extension cab. This amp is surprisingly quiet for 220w and there is no way to add a speaker. It is my understanding that the internal speakers are at 4 ohms. The amp sounds good but is just too weak for live use.

Amp 2: Peavey Combo 300, 1x15. 200 or so watts with the internal Black Widow speaker, 300 watts with an extension cab. The internal speaker is at 4 ohms and it can run another 4 ohm cabinet for a total load of 2 ohms to get the full 300 watts. This amp is LOUD, even with just the internal speaker, but I'd like to have a little more headroom.

Box: Radial Big Shot ABY

Band: Drums (hard-hitting, loud drummer), Keyboards, Guitar (100w Marshall head, 4x12 cab, two 2x12 cabs, although he doesn't run it at full volume).

Music: Rock/Blues/Jam

Thanks!

[lomo]

I'd use the AB splitter. There will probably not be a sig volume difference between the 2 options.