DSS is sort of a generic term, in that it refers to any hardware which is used to receive programming from DirecTV. So DSS and DirecTV are used interchangeably -- they're not exactly the same thing, but one is useless without the other. But "DSS" specifically refers to the hardware, which I assume is why doliver stated the question in that way.

DirecTV and TiVo are already integrated, in that TiVo works with existing DSS receivers. It would just be more convenient to have a single DSS receiver that had the TiVo unit built-in.