You would not need to find an icon for xplorer². TrayIt uses the native xplorer² icon. Also icons in the System Tray can be hidden. You’d only need to display the xplorer² icon. It should be easy to target with the mouse then.
I use a program launcher called MomShell. It is installed in the System Tray. I use it all the time to launch applications, often up to 20 applications together. Some of these are automatically sent to the System Tray. This spares clutter and works perfectly on a 19” monitor with a 1024x768 screen resolution. Of course I cannot say about 1600x1200 resolutions, but maybe habits are with us only so that they can be outgrown...

Anyway, until xplorer² has an option to run as a single instance, you’ll have to use it as it is, or choose the only alternative that seems to be available, i.e. TrayIt.
Cheers
Robert