Mr Macann said in the end the two judges were clear about the final group and voice potential was a big factor.
"We have six very strong finalists, any of whom could take away major prizes. It will be a wonderful grand final with a mix of great voices and high performing charisma."
Mr Thurston, who is living in Wellington, will be up against Aucklanders Benson Wilson, Edward Laurenson, Isabella Moore and Bianca Andrew and Oliver Sewell of Wellington.
The Lexus Song Quest has launched the careers of some of New Zealand's most celebrated opera stars including Dame Kiri Te Kanawa and Dame Malvina Major, Jonathan Lemalu, Madeleine Pierard and Phillip Rhodes.
The grand final is considered one of the most exciting nights in the classical music calendar with the singers performing alongside the New Zealand Symphony Orchestra and pianist Terence Dennis.
The winner receives a study scholarship of $15,000, cash prize of $10,000, plus a return economy international airfare.