'HDTV Ready' means that the TV can display high-def resolutions but does not contain a built-in HD tuner. If you get the HD via a cable box or satellite dish the TV can display it.
TVs labeled 'HDTV' instead of just 'ready' contain a built-in tuner and are able to receive 'over the air' HD signals via an antenna. [Some stations broadcast free HD over the air].
You only need a digital output on the TV if you are using the built-in tuner of the TV. If you are using a cable box or satellite dish, you would connect the audio directly to the receiver.