I've been using the IE Net Renderer website as I don't have IE6 installed.
Using this website with your Pro gallery, it generated a blank page for IE7 and IE8 (as the website doesn't display Flash) but when selecting IE6 it displayed the fallback text 'Requires Javascript and Flash...' which implies that it won't work (I don't get this text when selecting IE7 or IE8).
Having just tried your non-Pro gallery, I get the same results (fallback text with IE6 rather than just blank screen with IE7 and IE8).
However, you claim that the non-Pro gallery actually works in IE6 so I guess the results from IE Net Renderer are inconclusive.
If the non-Pro gallery did work, then swapping out the swf for the Pro version shouldn't have made a difference.
With regard to your other questions:
Can I define the displayed Browser title and the complete background color with the pro version?
The browser title goes between the <title></title> tags in the <head> section of the HTML page.
The background color can be set using the Flash parameter bgcolor... something along the lines of:
<script type="text/javascript">
var flashvars={};
flashvars.galleryURL="gallery.xml";
var params={};
params.bgcolor="#ffffff";
swfobject.embedSWF("simpleviewer.swf", "flashContent", "100%", "100%", "9.0.124", false, flashvars, params);
</script>
Steven Speirs
SimpleViewer Support Team