Yeah, softimage render preview window is much better.
*Sorry, my sarcasm here is just a result of countless times i asked myself how the hell did they manage to make it so primitive and keep it that way for so long.
I may have an idea how they managed to make it so primitive: XSI, when first came out, was targeted at big studios with lots of TDs - in an attempt to regain its users back from Maya - so previewing was not as important as the versatility to work with batch rendering in a console medium while previewing progress with imf_disp. Anyway, this is my pov so don't quote me on this.
I have no idea though why they didn't step into 21st century meanwhile.