Update:
Just to update:
TA has been unable to book tickets because AA will not let him know the correct 'price' for the ticket since the ticket was 'exchanged' by AA for some unknown reason resulting in the voiding of the previous eticket number and my new ticket number having a 'fare' of "exchanged".
QF, contrary to the repeated statements on this thread and elsewhere on FT have told me repeatedly that they cannot sell me an INF ticket since the original ticket is an AA -plated ticket.
AA themselves give wildly different answers every time I call but the 'theme' seems to be about €2000 each way for tickets I can buy on the QF website for €400.
I'll keep HUCA but this is now going on for weeks/months with no sign of light at the end of the tunnel.