There are some related threads on this subject but they're fairly old. Someone requested that I start a thread here on this since I've been successful in doing it. What I have is kind of a hack but it at least gets me a buffer so I can start watching a program 20 minutes after it starts and fast forward through the commercials.
I picked up a pretty old recorder, a Sony SVR-2000, about the time of the digital TV conversion. That one apparently is old enough so they didn't lock out the recording function when the unit doesn't hava an active account, Is this a Series 1? This one was mostly a cut-and-try job, but it was pretty easy because this one has straightforward setup for someone who understands how the pieces go together.
I told it that I had a cable box and from there it gave me a choice of using either the RF or video+audio inputs, and when it came to making the converter change channels from the IR output of the TiVo, it was just a matter of picking out the right one of a few intelligent choices of cable box manufacturer. I'm using an Insignia (Best Buy house brand) which is the same as a Zenith and is made by LG. I tried Zenith first, then LG, and with that setting, the converter followed the channel selection buttons on the TiVo remote.
The channel lineup that it gets by phone (I just picked a cable company at random, I think Comcast) is all wrong, but since without an account, which gives you the option of selecting programs to record by name and date, it doesn't matter. I can "Record by time and channel" and it works.
The newer Series 2 TiVo-branded unit that I've been fussing with lately is a little different. It's designed for a deeper level of dummy to set up. The list of cable companies and boxes is huge. While the cable or satellite service provider only matters if you want the station names or call letters to line up with your familiar channel numbers to line up, it's easy to guess the wrong box that doesn't work properly with the remote control.
The way to get around this is to let it go through its series of channel changing tests which it will almost certainly fail. Answer "yes" to everything for the shortest test sequence. Then, go to the Channels menu, then Channels Changing, tell it that you have a different box, and go to the Advanced Setup. This is where you can directly enter a 5 digit IR sequence code. This URL
has a long list of DTV converters and their IR codes.
The software needs to know what to do with each code, and not all software versions know all the codes. I had to let mine get an update before it had the code for the Apex converter that I was using on this one.
So, yeah, it's not straightforward. Hooking up the DTV converter so you can watch live TV is trivial, but getting it to change channels with the TiVo remote so you don't need to use more than one remote takes a little research and experimentation.
I assume that if I wasn't such a tightwad and paid for an account, I'd have a semi-functional TiVo, but because of the "dummies" setup on the newer models, if you tell it that you get your reception over the air, it assumes that you don't have a cable box but and doesn't give you the option of choosing one and you therefore can't get to the IR code setup from the menu.
One rub is that some DTV converters want to see a dash between the channel and sub-channel and the TiVo doesn't send one. My Insignia converter will work without the dash (264 selects sub-channel 4 under channel 26) but the Apex doesn't, even if you tell the TiVo (in the guided setup) that your box uses 3 digits to select the channel. So if I want to watch anything beyond the base channel (25-1) I need to use the converter box remote. It's not perfect, but for me it's good enough.
For what it's worth, I chose Cox cable and a Scientific Atlanta cable box, let it do its thing, and then put in the correct IR code once I found it on the menu. In my area (Washington DC) the channel lineup for the local over-the-air channels is pretty close so when I select the NBC channel it displays NBC, not that this matters.