Budget DAC for Oppo VS. Orig. Rega Planet

Hi,
I have an Oppo 970 and someone had suggested getting a separate DAC for my Oppo to improve it. What would you suggest in a separate budget DAC and digital cable? Would the separate DAC/Oppo combo be better sounding than if I just sold the Oppo and got an orig. Rega Planet? Overall, I've been pretty happy with the Oppo, although it is a little lightweight sounding. Thanks for your replies,
Louis