The TiVo HD only needs ONE Multi-STREAM CableCARD to allow dual tuner features.
The CableCARD goes into the TiVo and not into the TV.
Comcast came over today to install my CableCARD.
After I purchased the TiVo HD, I DM'd Frank on twitter at @comcastcares.
He confirmed that I only needed ONE CableCARD. I told him that I could find out how to order it online. You can't. You have to call on the phone.
So Frank scheduled the appointment for me.
I set up the TiVo, so it would be ready to go when the Comcast installer arrived.
He came with TWO Multi-STREAM CableCARDs. He told me some people want two cards to blah blah blah two screens blah blah blah.
He confused me.
Based on everything I had read, and what Frank told me, I only needed one card to allow dual tuner features.
So I told him to wait and I called Frank on the phone.
Frank confirmed that I only needed one card. He explained further that in some of the older TiVo Series 3 units, TWO Multi-STREAM CableCARDs are used to get around certain problems. Those problems do not exist on BRAND NEW TiVO HD units.
So one card was installed and everything works fine.
I just checked Grey's Anatomy and 30 Rock recorded fine. At the same time.