First... gain clarity about ALL THE TASKS!
Why "tasks first" is important
As a Hiring Manager, you certainly already fully understand all the tasks your future employee will have to perform in his/her new job -- after all, you most likely already lead a team of colleagues doing this very job day after day!
It is of utmost importance that you share this insight with your recruiters! And you must communicate back to the clients, too, as nobody understands the daily tasks better and can hence deduce the actual skills and competencies at play better than you.
But back to tasks -- a recruiter's job is not only to find the right talent and make them an offer - it is all of that PLUS making sure the candidates will ACCEPT our offer! So, you and the recruiters also need to sell the job to an interested candidate, and any decent candidate will not want to know which competencies he will deploy, but ask you (and the recruiter) for the actual job s/he will be doing.