Thanks for replying, satpro.
I do use DirectTV local. (I also tried Dish local for kicks; however its local station numbers aren't quite as accurate as DirectTV in terms of matching up to the OTA numbers.)
I'm using a Channel Master CM-7000, not the RCA box, so the IR blaster code is 0144 which I believe is a Pioneer code.
If I set the IR blaster via fine tuning to send a minimum of 1 digit (or 2), then for any given channel in the Program Guide, it sends the main channel number, and after a delay the CM defaults to subchannel 1 of that channel. E.g. if I set the DVR to channel 4, the CM receives 04 and then tunes to 4-1. If I tune to 20, the CM receives 20 and then tunes to 20-1.
However I don't think this allows me to set up manual records of subchannels of channels 1 through 9 (in my area, that would be 2, 4, 5, 7, and 9). IIRC you wrote that with your setup you could get the DVR to switch the RCA box to channel 2-2 by tuning the DVR to 0022. If I do that from my remote--or, it seems, from the manual record menu--the DVR just switches to channel 22 and sends 22 to the CM, causing the CM to try to tune 22-1.
I can tune to sub-channels above 9 this way. E.g. if I want 44-2, I just set the DVR to 442; it sends 442 to the CM, which tunes 44-2.
The only alternative I've found is to set the IR blaster to send a minimum of 3 digits. With this, if I want e.g. 2-2, I tune the DVR to 22 and it sends 022. If I want 22-1 I tune the DVR to 221 and it sends 221. The problem is that the Program Guide is now useless for tuning or recording. E.g. if I use the Program Guide to go to channel 2, the IR blaster just sends 002, which the CM nonsensically believes to be channel 00.2. A little more reasonably, but still wrong, if I use the Program Guide to go to channel 44, the IR blaster sends 044 and the CM tries to tune 4.4.
Basically I'm surprised that your setup is letting you tune channels 2 and 22 from the Program Guide and channel 2-2 via direct input, but the RCA box and/or the IR blaster operation for the code associated with the dta-100 may just work in a way that gets around the issues I've encountered.