It sounds harsh (a bit telephone like). A lot of your instruments are all peaking in the harsh area of the mid (around 2000-4000 hz). The piano sound hard, too hard for the context. It would be nicer in the mix if softer and peaking more in the mid (around 500-1500) than here in the hi mid. Let the place in the hi mid and treble for the strings. Your strings rhythm part sound fake (samples repetition and not the right bowing anyway). Try something more staccato or marcato and try to use a maximum of different samples when the same note play. Try to attach notes and make expressive lines in using many bowings (slow, legato, expressive, lyrical, vibrato, non vibrato etc). Don’t hesitate to use MIDI control (expression, volume, modulation etc) too. Your strings need to sing their lines not being robotic. That said, your cellos are pretty expressive and realistic.
I hope it helps!