(9.62) (Samkhya) “When no sound is present, the consciousness enjoys other objects such as visual forms.”
But if it is permanent, why does it not continue to apprehend sound?
(Samkhya) “Because there is no sound in the vicinity at that time.”
Well, if there is no object, sound, then there is no subjective apprehender of sound!

Shantideva’s point here is that if there is no subjective apprehender of sound then it shows that the consciousness has changed from there being a subjective apprehender of sound to there not being a subjective apprehender of sound, therefore the consciousness that the Samkhya’s is the I is not permanent.

(9.63) Moreover, how can an awareness whose nature it is to apprehend sound
Also be an awareness whose nature it is to apprehend visual forms?
(Samkhya) “It is like one person who can be considered to be both a father and a son.”
But this is mere imputation; he is not by nature both.

The Prasangikas do not disagree that consciousness can be aware of both sound and visual forms, they simply disagree that such a consciousness can be permanent. How is it possible then for us to refer to a continuously residing consciousness that the Prasangikas believe in? How exactly is that different from what the Samkhyas are asserting? The Prasangikas agree that the continuously residing consciousness is like one person who is considered to be both a father and a son, but that this difference is one of simply mere imputation by mind. The consciousness apprehending sound and the consciousness apprehending visual forms are two different consciousnesses because they are perceiving two different objects, but conventionally we can refer to them as our continuously residing consciousness by mere name or mere imputation. It is not inherently or permanently one or the other.

(9.64) The analogy of father and son does not work for you Samkhyas.
According to you, the independent creator of all manifests all forms.
Thus, father and son must be one nature, as must an apprehender of sound and an apprehender of visual forms –
But such things are not seen by a valid mind.

Once again, like the Christians, the Samkhyas believe in an independent creator of all phenomena.  Like many Christian Mystic traditions, the Samkhyas believe there is no distinction between the creator and its creation. Thus, father and son, the apprehender of sound of the apprehender of visual forms, must all equally be the same nature as this independent creator.

But how can there be an independent creator? If it is independent, then how could it come into a relationship with its creation? If it is permanent, then how can it create different things because does not it then change? Interestingly, it is only by embracing the Prasangika view that we can resolve these contradictions and view all things as the nature of our mind which is the creator of all, and that our mind is empty which enables it to change and create and come into contact with and know different things. We are able to make a nominal distinction between the mind that knows things and the objects that are known while still seeing them as being of one nature. All things are the nature of mind, and the ultimate nature of mind is emptiness.

(9.65) (Samkhya) “It is like an actor changing roles and being seen in different aspects.”
Well, if the I changes in this way, it cannot be permanent!
(Samkhya) “Although the aspects change, its nature remains one and the same.”
But you cannot establish an unchangeable nature of the I, because you deny the ultimate nature of I, the lack of a truly existent I.

Remember, the goal of the Prasangika refutations of the other schools is to gradually guide people to the Prasangika view. We do not disagree that it is like an actor changing roles but being seen in different aspects, we just disagree that such an I is permanent. We also do not disagree that although the aspects changed the nature remains one in the same, we simply say that the nature of that I cannot be truly existent. The only way in which the aspects can change and the nature remains one in the same is if everything is empty.  We can see the Prasangikas agree with much of what the Samkhyas say about the I, they just simply disagree with it being permanent and it being truly existent.