Tua is a beast, I'd love to see him in K'1 but I do think reach would be a problem to a certain extent. Still he has enough skill and certainly enough power to KO anyone there. I doubt he will leave boxing now though, how old is he now? 35+ atleast now.
A lot of these kickboxing champions in most countires are actually complete shit. Remember Pudz's first opponent? Ye, a Polish kickboxing champion.