Well, the installer just left and after much discussion of options, I went ahead with the original plan to just replace the single LNB dish with a three LNB dish.
He agreed with the first installer that he couldn't mount the AT9 or the Slimline at the same location as my present dish. While the Slimline is smaller than the AT9, the mounting hardware is the same, so there's not a big weight advantage. My present dish is mounted on a mast that I had installed when the house was built, and is very sturdy-- and while he could use that mast with the three LNB, he wouldn't be able to use it with an AT9. He couldn't install a new mast on the house due to company restrictions on installing them on stucco walls, my tile roof is unsuitable for a roof mount, and there are just no other mounting sites on the back of the house that would work.
Unlike the previous installer, though, he did give me a couple of alternatives: a tall pole mount, or a mounting on the flat roofed garage on the north side of the house (the pitch of the roof behind the garage would still allow line of sight to the satellites).
Neither alternative is particularly appealing. My wife doesn't want the pole mount because of the aesthetics; mounting the dish on the garage on the front of the house means finding a way to get the wiring back to my existing prewire setup on the rear. He said they'd just run the cables over the roof, but that's a little too Rube Goldberg for me.
I'll live with the present three LNB setup for awhile and see how it goes. I'm still waiting on an HR20, if I get that and they activate OTA on it soon, I should be in pretty good shape.
