I'm using Qa-al as well, although my players haven't encountered him yet. It looks like he only gets one shot because of the reload time of his weapons. Since he has rapid reload, it only takes a move action to reload his pistol or musket, hence the limit to one shot a round.
It would make sense to give him a slight modification using a weapon cord on his pistol or musket. Holding both guns in his hands, he could open with a shot from his pistol, drop it as a free action which is then caught by the weapon cord, then use a second free action to grab his musket with both hands and fire a second shot.
It takes a move action to retrieve a weapon on a cord and a move action to reload each weapon. Qa'al could continue wielding his musket in the next round and reload it with a move action before firing, but he would have to use a separate round to retrieve and reload his pistol on the weapon cord.
For last night's session, I decided to combine Qa'al's ambush with the "N" encounter from Assault on Longshadow.
I used the "Elthin Bluesteel" figure from Reaper Minis for Qa'al.
They had a good scrap and he left the party gunslinger lying in a pool of blood with DEX bleed ongoing. His cohorts were killed, but Qa'al escaped to fight another day.
I will most likely save him for somewhere near the end of book three. He's like the blond James Bond underboss.