Help, Manley Mahi, Oppo-BDP93

I'm using my Manley Mahi mono-blocks with an Oppo-BDP93, using the volume control via the Oppo. My speakers are either Zu Druid Mk04.8 or Dunlavy SC1 depending upon the need, per evening, or artist/recording. My question is; what DAC will better the internal DAC within the Oppo, and/or is my source the issue? I'm using the Oppo with WAV files via an external drive and still listening to CDs and Super Audio CDs.
Audio elitist,

"My question is; what DAC will better the internal DAC within the Oppo, and/or is my source the issue?"

What is the issue? What don't you like about the sound? Could it be you missed a step along the way (preamp) and the sound, even though it is clean, seems to be lacking body and overall musicality?
Hi AE,

What is your budget? I own the Oppo 83 but only use it as a transport into my DAC. I think of a number of good DACs you may wish to consider, but it is budget-dependent. ARC DAC 8, Stahl-Tek Vekian, Wadia 7, 9, Zanden, [for some] older and newer DCS, Accuphase...all are truly wonderful SOTA world-class DACs...i have heard nearly all of the above, and they are amazing.
What is your issue? You have not stated it.
My guess is that you would be much better off buying a decent preamp with an analog volume control than adding a separate DAC to your system. Digital volume controls are lousy in my experience and I have had little success going amp direct from a digital source (DAC or CD player) into a power amp.

Manley makes some great preamps that would probably sound great with your Manley monoblocs...if I were you, I would look for a Manley Shrimp before plunking down a lot of money on an outboard DAC.
Mcondon has a good point...i re-read your original post. i would not recommend the volume control of the Oppo (at all)...use a preamp. The volume control on my Oppo 83 is terrible in comparison to the quality of the sound coming thru a proper preamp...and it gets better if you use the Oppo into a good DAC and then into a preamp.