Bruce, if you understand, as I suspect that you do, that the Buddha used
the word "atta" only in the conventional sense, why do you need to win
non-Buddhists over to your point of view? Without doubt, those who try to
prove that the Buddha taught a self outside of the five khandhas, or
within the five khandhas, have misunderstood something. They are not true
Buddhists, and are still clinging to self-view (sakkaaya ditthi).

I have spent 30 years trying to convince others of the need to practise
meditation in order to see things as they really are, but in the end,
those who wish to know, meditate whether I tell them to or not, and those
who don't wish to know, don't meditate whatever I say.

Even the Buddha was reluctant to teach the Dhamma, thinking that it would
be hard to win people over to this very subtle point of view.

The true Dhamma cannot be realised by logical reasoning, so no amount of
intellectual proof will convince others if they wish to cling to a self.
The harder you try, the more they will cling.