Smoothing of arcs and curves loaded from AutoCAD are controlled by the AutoCAD variables - VIEWRES, FACETRES and FACETDEV.
VIEWRES controls how smoothly AutoCAD displays arcs - the higher the value the finer (and slower) arcs are displayed in AutoCAD.
FACETRES controls smoothed rendering of curved 3D objects. It is related to VIEWRES - value 1 means the same smoothness as in arcs (i.e. VIEWRES), 2 means 2x smoother display than arcs. The default value is 0.5, maximum value is 10.
FACETDEV (or AECFACETDEV in older ADT versions) controls the rendering of facetted 3D objects.
Smoothing of 3D solids can be controled also in VIZ Render - through the setting: File > File Link Manager > Reload > Surface Deviation for 3D Solids.
Please note that smoother setting means also slower display. Segmentation can be also influenced by models too distant from the 0,0,0 origin point.