DX10 has been nothing but fail. Nothing runs better or smoother in DX10. The only game that plays faster in DX10 is Far Cry 2, but the input lag and microstutter make it a game breaker for me so I finished the game in DX9 since it was much smoother. To date DX10 has offered nothing in the way of better performance. Use DX9 and enjoy the games!! Maybe DX11 will be less of a PR stunt to sell an OS and actually allow games to run better. Don't worry, it's not you or your card - it's DX10
Your PSU is fine (its got 3 x 12v rails 16a, 25a, 17a) and the sound issue is a separate issue entirely. Get the latest drivers for your sound card.