To my opinion, you should drop all power weapons in your squads to use Harlequin's Kiss instead because Dark Eldars do not have good Armour Saves. Your Solitaire might do the same as he may claim to use his Powerblades instead of the Kiss if he meets an Archon and his retinue.
I would keep the three Missile Launchers for the Jesters because of the two ammos available (antitank and antipersonel). But pay particular attention to their deploiment... they MUST have targets to shoot at without spending a precious turn moving.
Because of the efficiency of Dark Lance fire, I would not invest in a Venom against Dark Eldars. Sorry Nevermore222.
Beware of the drug user Caracters in the DE army. They could cause you headache by using in CC a nasty coctail (Always Strike First, Reroll CC misses and +1 attack). With the possibility they also bought Plasma Grenades that nullify your "cover", an Archon would be able to make his attacks before a Solitaire. I lived the experience myself.
I see Harlies as a nice bunch of specialists. They are breach openers on a battlefront, but not in sectors densely equipped with multishot weapons or overmechanized. In fact, many opponents (especially Eldar and Dark Eldars) may easily build an anti-Harlequin force.
In the 2nd edition, they were far more versatile being even capable to generate their own cover with Blind Grenades.
Finally, I wish you to enjoy the experience painting and playing them. Many of my opponents that called them "sissies in spendex" were obliged afterward to revised their opinion. They are really mean when used by a competent gamer.