So... I did something and it works. Now you are telling me that it doesn't work, even if it does. Smart.
Just because it works, and it is not really how it should be used, doesn't mean it works nevertheless.
What I'm saying is that Apple ID X is signed in to iTunes on computer A. Apple ID Y is signed in to iTunes on computer B. If computer A authorises AppleID X and computer B authorises AppleID Y together, then there is a kind of loophole of sorts that will let you both have 2 different Home Sharings running side by side. I have gotten this to work, even if Apple doesn't want it to be used like that.
Anyway, Rich, have you tried my suggestion? I'm sure it should work.