This is how you could return your processor with specific system settings.

gistfile1.php

<?php
class MyGetListProcessor extends modObjectGetProcessor {
    public $classKey = 'className';

    public function process() {
        $data = array();
        $settings = array(
            'emailsender' => $this->modx->getOption('emailsender')
        );
        $data['total'] = count($settings);
    	return $this->outputArray($settings, $data['total']);;
    }
}

return 'MyGetListProcessor';

Weird that modObjectGetProcessor didnt work since it extends modProcessor. Maybe it was missing a required variable. Good to see you got this working anyway and thanks for posting back your working example.