Wow this one sounded great just as it is Mark ! Great work ?
I wouldn't bother much on the cello/violin sound as the sounds for this one were just right, just what this kind of pacy track needed, the dist guitar feel...
Yes, if you are aiming for a more orchestral kind of feel, maybe you would need to look for sound libraries that cover the whole range (double bass, cello, viola, violin) separately sampled. Raising or lowering the pitch ranges with Melodyne may not bring out the organic feel you need for these strings.
And oh yes, this track does so much have the live playing feel... really good one overall