That isn't entirely true. The 6-pin only requires 2x12v wires, and 3xGround. Most good quality PSUs have 3x12v, because they are really 6+2 connectors, AKA 8-pin capable. The actual specification for the 6-pin actually says "no connection" for the middle 12v wire. You can see the pin-out
here. The 8-pin on the other hand requires the middle 12v wire be there.
If he has a decent PSU, then using a 6-pin to 8-pin adapter is ok, but most PSUs that only have a single 6-pin aren't decent. So I wouldn't recommend it, and we can't even guarantee that the middle 12v wire is there on his PSU.