The quarks were always twitchy with 6s fresh off the charger, not sure if the caps would help that really- a lower charge voltage (95% say) works wonders aparently.
As for the caps, dont go with the novak module, thats the one that has been blowing up on hvmaxx escs ever since they updated it. The specs you want are:
25v (or 35v), low esr, 105*C, 2700uf (I wouldnt excede about 6000uf if you use several in parallel). A few examples:
one
two
three