Sorry guys, I got really busy with work and haven't had a chance to write anything up yet. I'm a software developer, and my client is a state Department of Education, so things are crazy right now with school about to start back. I'll try to make it more of a priority in the next few weeks.
I can provide you this summary. It may be scary to those who aren't comfortable editing configuration files and xml files.
I have a Linux box that is running zap2xml on it daily, downloading the EPG data from Zap2It.com. I have two accounts at Zap2It, one for each TV provider I need (one for OTA channels, and one for AT&T U-verse). The data from the OTA channels matches 1 to 1 with the OTA channels on the Edision box's USB TV tuner. I use the AT&T U-verse data for NHK World, which is included in their packages. The NHK world channel on U-verse has the exact same program guide as the NHK world channel on 103W, so it doesn't matter that I don't have U-verse.
I then have it run various commands to sort and merge the files into a single xmltv.xml file. I then have a web server on the Linux box that hosts the xmltv.xml file so the Edision box can see it over the network. There is a possibility that zap2xml could be ran directly on the Edision receiver, but I have not yet tried. It would need the correct version of perl, zap2xml, xmltv_util, crontab or other scheduler.
On the receiver, I have the enigma2-plugin-extensions-epgimport package installed. This is included in TNAP 3.0, but el bandido has removed it from TNAP 3.2. I tried to convince him to put it back, but he refused because "no one uses it." In order to get it installed on TNAP 3.2 you have to do some voodoo. I did this late at night and didn't document it, so I'll try to remember when I write this up in more detail. I seem to remember having to downgrade TNAP to 3.0, install the package, go copy the file out of the install cache, and then upgrading to TNAP 3.2 and then manually installing it.
I then have a custom.sources.xml that lists my two custom sources: sat.channels.xml and ota.channels.xml. My sat.channels.xml file maps the enigma2 ID of the NHK World channel on 103W and the ID of the U-verse version of the channel on Zap2it. My ota.channels.xml maps each of the enigma2 IDs for the OTA channels to their counterpart in Zap2it. I then configure the plugin in the UI to do an import daily. When it runs, it goes and gets the xmltv.xml off of my Linux box over HTTP, then loads it into the EPG. This gives me about a week of data for NHK world, and gives me about a week of data for the OTA channels. I HAD to do this process to get *any* data for NHK world, but it was optional for OTA. Even though some guide data is broadcast along with the OTA channels, it is usually only good for 2-3 days, the program descriptions are very short (what I get now is much longer and more descriptive) and I don't have to set up any process to tune to each OTA channel daily to populate the guide.