Duh, you did mention all of that in the OP, must have forgotten, sorry. Well, given all of that, I think the OC-3 would fit the bill rather well. I'm pretty sure that wouldn't even worry about splitting the signal off at all.
The whole point about splitting it off, btw, was partly to help mix it on the board, but also so that any additional and separate processing done of the "bass" was as whole and natural as possible. The octave signal, absent any dry signal, does not sound very much like a bass guitar..., ahhh, about as articulate as a bodhran, so to speak
. It is still a benefit to micro-manage its input on the mixer, but not totally necessary.