Yeah, the SS preamp is very nice, no doubt, but that head does weight a bit more. I thought you were trying to minimize weight.
One thing to keep in mind about the Low-B2 though is the extremely poor sensitivity. You really need a lot of power to open these guys up. That's not just from the specs either, it's something I can personally vouch for.
As for the weight difference, the NeoX 212 is actually 59 lbs, not 62 as represented on the GB web site. So it's only 9 lbs more. It is a little bigger, though.
I personally don't think the Low B2 will sound as big as the NeoX 212. It's the same principle as the Eden 210xst. Sure it was deep sounding for a 210, but it's still a 210. It wasn't nearly as deep sounding as the 212xlt, and the 212xlt didn't sound as big as the NeoX 212 to my ears.
All IME, IMO. Happy hunting!