I'll throw my 2c in and hope I don't add confusion.

The Mega Live .... as it is being advertised .... it an Ethernet device. This is the same as the original 360 ... and since the original 360 was just an Ethernet device, any device on the network could utilize it.
The Mega 360 is not an Ethernet device, it has to connect to the transducer port of a Mega SI+ or DI+ unit .... and then that unit can share it across the network like any other transducer would be.

Since Mega Live is an Ethernet device .... like the original 360 was ... it is not really "connected" to a particular unit in the way the Mega 360 was ... but, as Rickie stated, they are currently showing that only Mega + imaging units will be compatible.

I don't know why the Mega Live is only listed as compatible with the Mega + imaging units.
We could hope that the compatibility could be expanded in the future since it is an Ethernet accessory, but maybe there are reasons because of the way the data must be processed that only those units will be compatible.

Gonna have to wait and see.