don't have a lot of time right now, so if you have more questions feel free to ask and I'll check back when i have more time, but this link should help.
Tech Portal : 625
then click on the left under "install" and then pick "dpp twin with seperators"
it should give you a good diagram.
The Dish Pro Plus LNB will control your other receiver too, but you'll have to run another line off of port 2 to it. Use port 1 for your 625. The Dish pro plus has another connection on it by itself, but it is an input, do not use it. Use port 1 and 2.
Port 1 can feed your 625 and you can diplex the second side of that to another tv. Port 2 can feed your other receiver just fine.
I don't know how easily you have access to RG6 cable, fittings, cable clips, etc... While it's not difficult, I'm wondering if you might consider calling dish and just seeing what it would cost to have someone hook it up for you from them. I wouldn't be suprised if it was close to $100 or a bit more, but I could easily be wrong, however by the time you consider getting a ladder to get to your dish to replace the LNB, buying fittings and a tool to crimp them on, buying RG6 wire and other accessories, you may be ahead of the game. If you have all of that already or can easily get it for not a lot of money, then tackling it yourself really isn't that difficult and there are tons of really helpful people on this site who should be able to walk you through just about anything.