There is still a sensitivity problem if a splitter used as a combiner after both preamps. It occurs because any front end noise contributed by the preamp connected to the mis-aimed antenna adds to the noise of the preamp of the marginal signal. To get any advantage, you could either notch out channel 19 from the mis-aimed preamp output, or attenuated the output of that preamp by enough to allow the desired signal to override the undesired noise. If you opt for an attenuator, a good place to start would be 6 db.
If you opted to filter the noise from the mis-aimed antenna, Warren electronics says that they still have some channel 19 Jointennas.
http://www.warrenelectronics.com/ant...Jointennas.htm
A Jointenna may only allow channel 19 through, or not; you'd only know if you tried it.