There is actually another solution that I did - screw trying to do this crap thru the AM21 altogether & get a cheap Tivo Roamio OTA DVR w/lifetime service! (note that this also applies to E* receivers, since they stopped providing EPG updates on new subchannels these days...although their receivers DO at least allow OTA scanning, but even it doesn't work the best, either)
While there is the obvious upfront cost (they were going for $300 a couple months ago) you would have 4 completely separate OTA tuners that would leave ALL of the D* tuners available for satellite channels, which would obviously cut down on potential recording/viewing conflicts thru the D* receivers. You would have an EPG that would be always be properly updated w/out having to resort to all the goofy fake-out tricks people are doing w/the AM21, & you wouldn't have to worry about D* deciding to change things one day on the AM21 & causing more issues. (like they did when they removed the OTA scanning feature on the HR34's

)
Honestly if you're in a market that really has THAT many OTA channels, IMO it would be money well spent.