I'd give TiVo a call.
I don't see why they wouldn't support the AFN, that's just unAmerican.
Zap2it has the AFN listed as a provider, TiVo and Zap2it both use Tribune Media as their program guide source.
I found the AFN on Zap2it by inputting 10101 as the zip code.
Panasonic Viera TH-46PZ800U 46" Plasma
TiVo S3-65 HD Hrs-LT
TiVo Roamio Basic 300 HD Hrs-LT
TiVo Roamio OTA 75 HD Hrs-LT
TiVo Roamio OTA 400+ HD Hrs-LT
Harmony 880 Remote Control