I just switched from DirectTV to Comcast cable a few days ago so I'm still figuring out what all I can and cannot do, but so far it's worlds better than trying to use a satellite provider. I now have channels 2 through 99 on my TV card (analog only) as well as channels 2 though 99 via firewire. Using my TV to scan, it appears I could use something like HDHOMERUN for additional digital channels, but no where near all the channels I can get via STB and I don't know how well the channels would match up to Schedules Direct (lots of manual work to get them matched up I'm sure).
Why do I want to keep the STBs on the two main TVs? First, HDTV. Most (all?) HD channels are above 99. HDHOMERUN could probably pick of some of these, but not all because most of them are encrypted. Second, additional STB functionality. Loads of channels only available via STB plus Comcast has a pretty cool feature I never knew about, free on-demand movies. Some great older flicks that I've never seen, but watched just because they are there. As far as I know, there is no way for LMCE to control the STB and access on-demand.
I could use a HD component capture card to copy the HD output from the STBs and put the STBs with a MD/Core somewhere out of sight and that would take care of the HD output and all other channels. I'd still be left without easy access to on-demand movies, but everything else would be addressed. However, those cards are not cheap (yet), so for now I'm going to use s-video output from the STB for any channels above 99 where I want to record a show (SD only), and simply use the STB for live HD content and the free on-demand stuff. This is the plan at least, I'm not quite there yet.