Adding a second tuner card to W7 MC. Do I just pop it in and am good to go?

IIRC ATSC is terrestrial (broadcast) TV, right?

To the tuner, the antenna is pretty much a passive device (as opposed to a satellite LNB which is controlled by the tuner for selecting transponders, etc)
so assuming there is enough signal strength, the lead can be split multiple times. A simple 1-to-2 splitter isn't going to degrade the signal significantly. I am doing this in my DVB-T scenario without any problems at all.

Just plug in the second tuner. If it is identical to the first one, it will just be picked up as a device in Windows and then Media Center will see there is a new tuner and ask you to configure it.

You will have to do the Media Center TV Setup again, though, including channel search, etc.

There is no difference in using same or different brand tuners. Each tuner stands on its own merit so which ever tuner you get make sure it is a well made and has had good reviews from other users. The three important things to consider are:

1. Is it supported by the software you intend to use (in your case W7 Media Center)
2. How good are the drives (stable or cause crashes)
3. How sensitive is the tuner (sensitive to low signal, multipath etc)

I would recommend this one. http://www.newegg.com/Product/Produc...82E16815100041

It is a dual tuner so you get two additional tuners on one card so that you can record a total of 3 shows at the same time and the price is reasonable ($59) and it works well in W7 media center.

+1 on the Avermedia Duet. Awesome little tuner, especially for the price.

Just ordered another Duet today as well ;-)
Get the whitebox since you have w7mc, you won't have to deal with the rebate. Shipped to CA w/ tax was 70 bones for me, and its PCIe, :-)