Gotcha, nice diagrams.
Waht I would do.... Use the TV 3/4 setup to do all my recording... use Single mode on that reciever.. since both TV's are in the same room and wont be watching anything seperate.. this gives you the option to A record something in the background B record 2 things at once while no one is in the room and C a nice PIP feature on the TV and Prjector. I would run ouput 2 of the 3/4 reciever via Coax to the External antenna in on the other DVR. that way when you turn off the tuner that is on say tv 2 on the 1/2 dvr the dvr from downstairs passes through and you can watch whatever is on that dvr (the tv 3/4 dvr that is)
what this does:
As noted it gives you the functionality of PIP and background recording on tv 3/4
It also allows you to watch all that is recorded on the 3/4 Dvr on tv's 1,2,3,4. I really hope this helped.
My recommendation is not to have a DVR on tv's 1 and 2 inless you want to record alot on those tvs and couldnt record downstairs. I would get a 322 for tvs 1 and 2 and that way your wife doesnt have to worry about disrupting a recording if she uses any tvs.
hope that helps.