I'm still curious about creating my own theme for GameEx, as well as choosing my own screen saver, but...well, as stated last night, some sleep lent itself to solving my problem very well.
Upon reading the documentation, I thought I'd discovered my problem...there is a setting for all other emulators in which you may turn the desktop "on" or "off" as it starts. When I turned the desktop to "on" I finally had my picture!
However, I wasn't thrilled with having to move to full screen every time manually...and that's when I discovered that PJ64 has a setting that, when checked, allows the rom to start full screen. Once that box was checked, I went back and set the front end to "No" on the desktop setting....and I still have my picture!! YAY!!!
A shoutout to the creator of this front end. It works awesomely - so far - with the IPAC set I'm using right now. No need to change / adjust anything...just installed the program and ran it!
Course, my wife isn't going to be hjappy with it until I get the dragon wallpaper up as it's background.
