I have an original B2, I guess that's a Series I, right?
If your B2 has aluminum edges and no Speakon jack, yes, it's a Series I
Is the new B2 any different? How will the two sound together, or are they basically the same?
The Series II cabinets have black edge protectors, a different tweeter (IIRC) and a different crossover that doesn't allow you to turn the midrange and tweeter all the way down.
I currently put my Aguilar DB750 through the B2 and an Eden 210XLT. The Eden of course overpowers the Acme, and I don't like it.
I don't like Eden cabinets either
I want to go with 2 cabs. I'm definitely getting rid of the Eden.
Should I get another B2? Or should I get rid of both 210s and go with a pair of Aguilar GS112 cabs? Which combo will make my Bongo4HH/Jazz/6-String with Barts DB750 sing best?
If you enjoy the clarity that Acme affords, you might be disappointed with another cabinet.
I've never played through GS112s but I understand that they're rather dark, some describe them as muffled. Again, if you love the Acme's clarity, you might not like them.
You'd need lots of power for two B2s...perhaps up to a Kilowatt.
Not sure what you mean by "sing"...

