i have a Series 2 Tivo hooked up to my 522 (because of the Tivo-To-Go features) and it works ok... you will use a IR blaster to control the receiver, and occasionally mine misses a button or two, causing it to change to the wrong channel... also, occasional problem with the 522 turning itself off overnight and the tivo wont bring it back up... you have to use the Dish remote, or setup a timer to go off after the updates are done
I have ended up using it as 2 recording devices, the Tivo has the Tv1 side, and I use the Tv2 side to record other stuff
all in all i'm decently happy with it, I like the networking features of the Tivo, but I hate the guide... it is painfully slow compared to the Dish receivers.