For the main, ".1" channels, you only need to use the virtual, non-decimaled channel number, like "7" instead of "7.1".
For the ".2, .3, etc." numbers, there's a way to do it, but you have to look up the details here. Maybe it only works with the 3-digit numbers, and you use something like "121" instead of "12.1". So with anything under 10, you might not be able to tune to the subchannels (which isn't an issue for me here, personally, because everything under 10's subs aren't anything important - mostly weather channels).
Something like that, anyway. I think the main Zenith/Insignia thread has some info on it, because people have gotten that box to work with an LG satellite box code. Unfortunately, my two older recorders don't carry the code for it (I bought the Zenith thinking it would work, but unfortunately, it doesn't). So if your VCR's are older they might or might not have it.
The RCA and the Channel Master boxes can also be controlled with an IR blaster. The RCA apparently uses some kind of standard RCA code and the CM uses a Pioneer cable box code. I know for sure that the Pio one is pretty old and very common. All of my recorders and remote controls have it.
I'll be using either both or one of my coupons on the DTVPal also, because I, too, want to use them with my older HDD/DVD recorders.