The manufacturer recommends a stout 15-20 watts generally. As for detail, they have it, they just don't make you notice it. IMO they are enormously musical speakers (the whole line), excelling at microdynamic/tonal shadings.
For very large rooms? Probably not.
And as for the OP's question, never heard the OBX, but actually I think the general consensus is that the jump there is not too big. When is the last jump in a line the biggest? Furthermore, the benefits of an outboard xover, being related solely to mechanical isolation, are going to be directly related to listening volume.
Going to the IBX is the big jump.
Perhaps the U.S. importer will chime in here.
