In my mental image every pair of hands is linkt to the brain, and has one strong an one weaker side. Or in other words it's all in your brain. Muscle memory a.s.o. is per set.
And I didn't said that, every guy with 6 arms can use them all the same (btw: that's a fact in cases of drones with mechanical arms, rigger or cyborgs haven't got that problem at all), I meant only that 2 or 3 times the Ambidexterity Quality do the job perfectly fine, and without the Quality you have for 15 BP (Shiva Hands) another strong and another weak hand (that's only fair, thinking about the "real" use and the given Freak Factor).
In matter of fact we discuss here a point value of 10 BP (or 20 KP), so usually it isn't the world but how I pointed out, that is in matter of the Character Generation unlikely a problem. (If you want a fully ambidextrous 6 arms guy from the start and don't want to use some house-rule because of that, you cannot do so if you need 5 times Ambidexterity).
Beside the drone auto-ambidexterity (whatever quantity of arms 2 or 20), there is another way to get a limited ambidexterity from the Martial Arts rules (see Off-Hand Training, Arsenal, p.160) and that rule apply to any off-hand at ones.