I would go very easy on the panning. If you listen live to a string quartet in a theatre, there isn't really much spatial difference for each player.

What you get in a well designed theatre is glorious mix of direct and reverberated signal.

I think this is why most classical music, whether full orchestra, or even chamber music or quartets, are not done with individual mic'ing, but rather stereo miking of the quartet itself, with any manner of the multi-mic stereo techniques being used.

I understand that's not how you did your recordings, but most well-done classical recordings capture all kinds of the room and that is part of the hair-raising experience of classical live recordings.