There are adapters that will convert a single 6 pin to a single 8 pin, but they are not recommended. They will allow more current to flow through the same wires thus increasing the heat dissipated by the wires. This is not ideal and does pose a risk. Instead, consider using an adapter that converts 2x6 pin to 1x8 pin, and also using an adapter that uses 2x4 pin molex to 1x6 pin in order to properly power your card. That is a nice card, don't cut corners powering it or you might regret it.