Hi Solo
Sorry can't help with renderplus logon I'm sure Al will.
Never had the issue with mirrored floors, could it be that Irender is picking up settings from other rendering engines and applying them?
The shadows can be changed via the cloudiness adjustment. The dark adjustment in sketchup has no effect with IRendernXt.
Link to help sunlight cloudiness page.
I tend to use the IRendernXt sunlight and sky settings rather than the sketchup.
You can increase the number of passes and time.The more passes the better the image etc, and you can increase the size of image render if that helps with AA. Maybe Al could chime in here.
Also you can set compression levels for saved jpgs so less lost of quality etc. You can also save out as pngs and the change the max texture size on the Special Tab can be set to 0 for no max.
There should be a setting on Special Tab to auto load.
Hope that helped for now, until Al can get you onto the forum