I’m not sure I understand your configuration. For an external cv you need to first assign a pot mapping source to Mod 1 or Mod 2. Then you need to connect a CV ( say an LFO output) to the Mod 1 or Mod 2 input jack on the front panel. Set the pot map destination and amount. That’s it.
On Pot Mapping, the digital data received from the A/Ded knobs is routed to the post A/D data of another knob.
The Pot Mapping was an additional feature not in the first Voyager specs.
Doing real CV mapping like you tried, would need plenty more A/D on all the CVs available on the connector to the expanders socket.
The pot mapping “source” IS a control voltage whether it’s a performance control like the keyboard velocity, mod wheel etc. or one of the pots on the front panel. You can’t modulate a control voltage with another control voltage. Think of the the Mod 1 and Mod 2 busses as open/spare unassigned sources until you connect something to their input jacks.
You are correct; but the LFO Rate CV input is a separate or rather parallel path to the destination. Just like you can modulate the filter directly with a CV. It affects the destination directly, not the pot mapped source.
You have several paths to most destinations:
The actual physical front panel knob
The physical CV input jack (if it exist)
The pot mappings (up to 4 although assigning more than 1 to the same destination is of limited use )
Mod 1 Bus
Mod 2 Bus
The Mod Bus inputs can simultaneously control the destination selected on the front panel as well as the pot mappings - pretty cool. But obviously you can only have one thing plugged in to each Mod bus input so maybe try midi CC? One thing interesting (had to try this out of curiosity): You can control the pot mapped assigned source with its assigned midi CC. Which I believe is no different than controlling the pot mapped destination directly with its assigned midi cc.