That could be the brackets, they are used for controlling the order items are evaluated. The brackets likely disappear, adding TriViAs instead of [TriViAs]. There are 2 solutions.
Option 1, 2 seperate commands with only 1 forward slash '/':
/avoice -w [TriViAs] #masterwarez
Option 2, 1 command with both forward slashes, but using $eval:
//avoice -w $eval([TriViAs],0) #masterwarez | avoice on