Add a preamp or a whole new integrated

Looking to upgrade and specifically looking for better sounstage with chamber and orchestrsl music. I have a smallish room and a small system that does really does great on vocals and folk music. Seeking to improve how it sounds with Vaughan Williams, Elgar, and choral music. Needs more separation, better dynamics (?)

I have a NAD 352 amd and Cyrus 8x cd player with separate power unit. Hero interconnects. Tetra 120u monoitors (top ported, love em) and a velodyne subwoofer.

Would i be better off keeping the 352 and adding a preamp (NAD 165, parasound 210, cambridge 840e on the list) or ditching the whole thing and getting a better integrated. Budget to $1500.

Thanks.