I've never played Splat!, but it sounds like most of the issues you're having can be fixed by editing your Splat! INI.
If you've never edited an INI before, don't worry, it's really not a big deal and it can even be done through the MAMEPlus GUI. I'll try and catch one of your streams soon so I can help out.
Also, DO NOT RESET, it will kill any recording you have initiated. My guess is you'll have to bypass the boot screen by pressing the Player One button, or you'll have to cycle through the service menus using F1 or F2.
We'll get you sorted and Splat!ting in no time.