I feel like this, the last line of the Split fire rule, shows that it is the unit making both attacks. If that is the case, then both should be valid assault targets also. Whilst it is not explicit endorsement of being able to use both shooting attacks, it is endorsement of the model being counted as the unit for it's initial shooting attack in the same way as a normal shooting attack.These must be at a different target, which cannot be a unit forced to disembark as a result of the Split firing unit's initial shooting attack.