the other problem since implement Chess960 on Arena are the Castle move input and output correct send to the engine, that "o-o" or "e1g1" out is not standard castle output for Chess960, only the king takes rook is standard.
On Shredder works Tornado very good and correct during playing Chess960 but on Arena not work in UCI mode, is also not work if i use polyglot.
i see also that Arena not sendig correct setboard position castle right if playing Chess960 ( not KQkq ! AaHh or BbGg sending the files who the rooks are is for castling )