Channel Master has come out with a new tuner, the 7003.
http://www.channelmaster.com/Digital..._p/cm-7003.htm
In theory, it is possible to add its SD analog output from one antenna system to your other system on channel 3 or 4 with the modulator in the 7003.
It is also possible to add its HD output to the other system with a modulator on an unused UHF channel. I haven't done either.
related thread:
Reasonable ATSC-->QAM Transcoding Option?
http://www.avsforum.com/forum/25-hdt...ng-option.html
My favorite way is still to connect antenna A to the antenna input of the TV and connect antenna B to the input of a separate tuner, with its output connected to the aux input of the TV.
If your "TV" is really a monitor with no tuner, then you will need 2 separate tuners.