I wish I had good news for you, but I'm afraid I really don't. Once Comcast implements its changed lineup, it looks like you'll be able to receive only the most basic channels using tuners like the EyeTV Hybrid and 250, but you'll lose access to "expanded basic" channels like ESPN, MTV, Disney, and Nickelodeon. That's because Comcast is about to start encrypting those channels, making them out of reach for your EyeTV unit. In addition, only devices that ship with built-in CableCARD technology, like TiVo HD, will continue to be able to tune in to those encrypted signals.
Although you can rent a digital adapter from Comcast and use it with your existing EyeTV tuner, you'll be unable to schedule recordings -- or even change channels from within the application. Instead, you'll have to use the Comcast remote to access all channel changes. What's more, if you get one of the Comcast tuners and use it with your EyeTV unit, you'll only be able to receive standard definition signals. That's may or may not be a huge deal for you depending on your love of HDTV.
If you want to keep scheduling and watching with EyeTV, you need to consider laying out about $200 for a new Elgato product that includes IR-blaster-based remote channel changing solution that works with your (optional) Comcast cable set-top box. The standard digital adapter is a different thing from the set-top box; you need to rent the latter to receive HD signals. Elgato has been working on this new product for some time, not just to address the Comcast situation but also for anyone who has premium cable or satellite TV services; i.e., any service that requires a set-top box to descramble channels.
This new product is launching this week and it's called the EyeTV HD. EyeTV HD is designed to work with HD cable boxes and satellite boxes, providing access to all the channels a user pays for, without restrictions. It does this by connecting to the component video outputs of the set-top box. It includes a remote channel changer cable (aka IR blaster) so that the EyeTV software can automatically change the channel.
You'll still need to rent an HD cable box from Comcast, so expect to pay several dollars a month in addition to any initial cash outlay for the EyeTV HD. Plus you'll need to figure out how to fit an entire cable box (figure about the same footprint as the iPad and maybe an inch and a half thick) and the EyeTV HD (let alone set up all the IR Blaster stuff) on the desk next to your TV-watching computer. It's an ugly situation.
Obviously, Comcast would prefer you to rent their DVR solutions. And it's getting harder and harder to roll your own. Fundamentally, Comcast's new policy means that older EyeTV owners are, well, mostly screwed. (The ZephIR IR blaster should work properly with Comcast's digital adapter and EyeTV, but caveat hackteur.) I wish I could paint a rosier picture of the situation, but I can't.