To get the additional HD channel pack with discovery, timeshifting, etc. you do need to subscribe to the analog pack which includes the channels.
Was going to add them primarily to get discovery channel, but would have cost $4.95 plus another $20 or so for the me tv pack I think it was. A bit much to add one channel I really want, and a bunch I don't really care about.
Same deal adding any of the digital channels. I tried to add the food network digital station, but was told I could not do it without ordering the analog pack which contained it.