According to retailer Solidsignal.com, the new Directv Tivo(THR22) will scan with the AM21, but I haven't seen any confirmation from a user yet...
http://www.solidsignal.com/pview.asp?mc=02&p=AM21&d=DIRECTV-AM21N-OffAir-Dual-Tuner-%28AM21%29&c=DIRECTV%20Receivers&sku=8546300063