Tivo S2 DT will display Premium but not Basic Cable

Hi, long time Tivo user first time poster...

Recently took my Series 2 Dual Tuner out of mothballs and replaced an earlier version of the Series 2, which I never had an issue with.

I use a Comcast HD/Digital Cable Box and know that I can't get true HD from the Tivo Verision I am using.

THe problem I face is that ever since setting up the new Tivo I cannot get basic cable (AMC/Bravo/VH1/CNN those types of basic cable) to display on my TV, but premium channels (HD Content and HD HBO.etc) play fine.

Cable runs from the wall to my comcast box and from the comcast box to the Tivo input and my Tivo has the A/V jacks to my TV... I didn't think I needed a splitter here but perhaps I am overlooking something. Not planning on getting a HD Tivo and just want to get this one to work. I have rebooted the Tivo numerous times as well as the cable box. The Tivo will occasionally show local basic channels but will usually show the blue screen saying that it has lost its signal. When this happens I can switch to the HD equivalent of the local channel (Fox for example) and the HD version will show fine (of course its not in HD). Changing between basic cable channels does nothing...

Any advice would be appreciated... my wife will kill me if she can't watch Top Chef!!