The thingy in question is a two-way amplifier, so I think it would help the b-only Soundbridges a lot. (And no, I don't want to attach a bulky external g module to them. That would kill the sexiness factor.)
I already have a 6 dBI external antenna, these old house's walls are thick!
RokuMike: Would a Pre-n router improve communications even with g or b products? I read a little demo on Linksys's site about exploiting signal reflection, etc. but I'm not sure that would help non pre-n devices. Would my two Soundbridges benefit?