Adapter cable to 8pin input
I bought an XFX RX 580 GTS XXX edition and I thought it would come with a 6pin connector, instead it has one 8pin input. With the card there's also an adapter 2X 6pin to 1x 8pin. However, expecting the 6pin input, I did get a second-hand Corsair VX 450W, which comes with only one 6pin PCIe cable and no 8pin ones.
Can I get another adapter, like 2X 4pin molex to 6PCIe for the second 6pin PCIe I need, or directly a 2X 4pin molex to 8PCIe? Will these options work and is there a big difference between them I should be aware?
I'm using the PCE164P-N03, so I only need 1x SATA cable from the Corsair, the rest is free to use.