My answers in blue 
pezdoctor said:If I get a new HR22 installed with a new dish (to replace my old dish), I assume I can keep using my owned HR10-250 with existing 2 cables and add 2 more cables from the new dish to the HR22? (i.e. ending up with 4 tuners using 4 cables from the new dish---and I don't need a switch since the dish has 4 LNBs built in, correct?)
Correct
Are there any compatibility issues getting HD channels from the HR22 and the HR10 at the same time off the new dish? (at least until the MPEG2 goes away, at which time the HR10 will still remain for OTA only and SD)
Nope, the slimline 5 sees all the satellites you need for all the HD feeds (MPEG2 110/119 and MPEG4 99/103)
[I will eventually go to the new D*TIVO unit, but for now want to run the new DVR while keeping the old DVR---and keep everything as simple as possible.]
Thanks,
Keith
