Actually, it turns out that the Empeg puts out a line level output at 1V and that's all the Bose head unit required. These monkeys just didn't do their research. Some kind fellas on miataforum.net provided the missing information regarding the spec of the Bose head unit that made it all much clearer. The Empeg is now installed properly and, if it is at all possible, sounding even better than the Bose CD player!