It is like a 410, except instead of satellite (whatever form of QPSK DCII the DSR400 series tunes), its digital tuner tunes QAM modulated cable, the headend being relatively simple "QPSK" to QAM converters, rather than more elaborate systems to supply DCT series boxes. It is part of a system called HITS-QT. Echostar had similar boxes for their platform, to do the same thing for small cable operators.
I don't think they are ever sold to customers, just rented.