XSI uses openGL for drawing most of the inteface.
DX is only available for realtimes shaders and it’s hosted.
XSI isn’t max, where the ogl implementation is sloppy and being win only they offer you to fall back to dx for drawing the interface, XSI is OGL based.
Refresh issues usually have little or nothing to do with OGL or dx, they are usually a videocar/driver issue.
Changing drivers and finding a solid release (latest does NOT mean greatest btw) is the first step usually, and 90% of the times the last as well since it will fix most issues.
If you use an ATI card you’re also in for a world of pain to find the right release that won’t have their selection lag problem, but it’s out there.
Searching the forum for previous similar threads (about graphic issues and videocard in xsi) will get you a wealth of information.