Thorsten Hartmann has worked out a workflow for using the 3dsmax daylightsystem with IBL and has created a post showing his findings. Check out the Workflow for using a 3ds Max Daylight System IBL and mia Physical Sky tutorial here.
Thorsten Hartmann notes: The 3dsmax mr_physical_sky don’t work correct. I have wrote a phenomenon to activate the “physically scaled sun” Function. If this Function on, have you a real IBL environment. To adjust the sun use sun disk intensity (sun energy) and sun disc scale + sun glow intensity (corona and shadow smoothness). You can now deactivate the 3dsmax mr_sun and mr_sky, and use only the IBL Mode, but you need the daylightsystem at the scene, to have the right sun position. This new mia_physical_sky phenomenon is included at my newest Shader Utilities Packet build (20110829).
