It depends on what kinds of wires you got. Look at the PSU cables, find the AWG markings.

You should supply the extender with 75W so if the molex cables have

AWG 22 - 20, you can attach 1 molex -> 6pin per cable
AWG 19 - 18, you can attach 2 molex -> 6pin per cable
AWG 17 - 16, you can attach 3 molex -> 6pin per cable
AWG 15 for 4
AWG 14 for 5
etc.

Most good quality PSU's come with at least AWG 18 so on those, 1 molex cable can do 2x 6 pin adapters or a single 8 pin adapter.