Just putting one spade through the hole is a very poor connection, very very poor actually as the hole is not flush and only a hairs breadth of contact is made. This will cause brightness and poor bass. You can buy locking banana plugs which are probably the best route, but nothing wrong with bare wire either so long as you use contact enhancer and/or trim a wee bit off from time to time. You could also change to typical WBT binding posts for a small fee and a little effort if so inclined, or even hard wire you speaker wire directly to the circuit board, which would be the ideal sonically.