well - I'm guessing you already know the biggest 'spoiler' - that awful creaky guitar with all the finger noise.
I'll try to help - First thing, forget plugins and processing. You need to get the mic positions sorted. The finger noise and creaky sounds are simply because the mic was in the wrong place for that guitar - note, not every guitar, but the combination of instrument, player and microphone take quite a bit of care and skill. Did you record the two players with one mic, two mics, or what? The cello has a lovely tone, but it's a bit distant and dark.
The snag I suppose is you didn't set yourself a framework. Is this a cello performance, with guitar accompaniment, or a duet, or even a guitar piece with cello accompaniment? You need a focus. If the cello is the featured instrument and that's a melody, not a harmony, then the dark tone suites it quite well - so it needs (and this is just my opinion) to be a little more prominent, less murky and miked in a way that enhances the nice playing and decent instrument. The guitar could then be the distant (or more distant sources) and brighter, and less mechanical noises.
I'm assuming that in the room, those creaks and finger noises were not so prominent?
You have loads of processing possibilities, but I do know exciters and dynamic compression would be way, way down my list for this piece of music. Clarity, and accuracy in your mic technique would be my go to features. Right mic, right place. Of course you could have all sorts of setup problems we don't know about. For this kind of recording, you get the mics right first, and effects and processing can be used to enhance, not repair. If you record this properly you might discover, the reverb is the only thing you need.
It's not bad, but I suspect just mic position issues that you tried to sort afterwards, and that rarely works.