Thanks to wikeeboy I have been trialling his Mutec MC 3+ USB.
I now have my head around the setup. It has a wide variety of internal selections and I have finally worked out what sequence of button pushing I need to implement, to get some great quality sound.
1st off the Mutec certainly cleans up the sound from the PC Lagoon via USB into the Oppo's USB. It bring's everything into greater focus - that's the simplest way I can describe it.
Because the unit has a variety of inputs I can toggle directly between the Units Coaxial and Optical outputs into the Oppo. After an hour or so of listening yesterday I think the Optical has it. The Optical Cable is the Lifatec Sitflex Glass version. The Optical just bested the Coaxial (Gary Cawsey 75ohm Silver core cable with Screw tight RCA connectors) in the area of clarity and refinement. It was smoother and yet still dynamic. Vocals are liquid.
I now have the Plasma TV running into the Mutec with a 2nd Lifatec Glass Siltec Optical. Getting sound (TV or Music) via the Mutec to the Oppo is just a matter of selecting the USB or SPdif output, both into the Lifatec output.
Still more listening to go this coming week but I am liking what I am hearing.