you have to plug them into an amp on the receiver. line level outputs won't cause the speakers to make any noise . . .
you can strip the wires and connect the 'raw cable' to the appropriate amplifiers on the Denon.
you might find it easier, assuming the Denon's terminal spacing is right, to pick up quarter inch to banana plug speaker cables and just plug them in. My sense is this is likely your best bet. Guitar Center or similar will have a range of such cables. Don't splurge. You're not going to be winding and unwinding these cables multiple times per week, so they needn't be the most, uh, robust construction in the world.