it allows you to plug another LNBF in via coax for say a wing dish.
This worked for me, I have a Dish500 antenna with a DPPlus LNB (This is a must). I used the dual tuner receiver to independently operate the two TVs in the Motorhome. Run one coax from the left side of the LNB to the "Park/Cable" in on the exterior of the RV. Disconnect the coax at the "Antenna/Cable" switch in the RV from the cable input side and connect it to the receiver using a Dish Seperator (Similar to a splitter, but provided by Dish, a regular splitter won't work.), and connect to Sat1 and Sat2 on the receiver. Run AV cable from TV1 output on the receiver to the video controller Sat in. Then run AV cable from TV2 output on the receiver to the video controller Aux in. Switch the controller to Aux for TV2 to view sat programing and use RF remote control. Hope this helps.
You aim at satellite 119. The trick is to insure that the 119 LNBF is being selected. The Dish 500 Pro has a built it switch and without a controlling 22 KHz tone, either cable can be connected to either LNBF.
Always make sure the mast is perfectly vertical. An adjustable leg tripod helps this a lot.
The hardest alignment in the azimuth because the signal focus is no where you think it is by looking at the dish. Right now people look at my dish and shake their heads because it looks like the dish is aimed into the back of the trailer. With 138 Skew and 38 Elevation, the focus is off to the right of the trailer.
The metal dish will cause a deviation in a compass close to the dish, upward of 10-20 degrees.
I have a lot of info on this at TV Dish Setup.
There's no such beastie as a Dish 500 Pro. There is a Dish500 and a Dish500+. What the OP is describing seems to be a DishPro Plus 500.