Yeah, we're gong to need more information. Lots.
You have way too many variables going on. Could have multipath in the bedroom but not in the living room. Could be that the converter box has more sensitivity (Lord knows my converter boxes pull in about ten channels my TVs don't). Could be that the signal in the living room is JUST weak enough that putting a splitter in the line knocks it down below what the TiVo considers acceptable.
Move the TiVo into the living room. Disconnect the antenna from the converter and connect it into the TiVo. If that doesn't work, then the signal's too weak or the multipath is too high for the TiVo to work with.
But before we venture further, need that location, TV Fool report, Make and model of the converter box... are you ground floor? What type of structure? What channel is Retro on? Probably a subchannel, but of which station?
Walking the fine line between jaw-dropping and a plain ol' yawn.