custom search for a custom post type

Hi Guys,
I have a rather big problem. I have created a partners community Index on and have a custom post type "partners" for that with some custom taxonomies to categorize the partners.
I created a page template and got all the partners displayed there in the way i wanted. So far so good. I was also able to add an Index-Feature.
What has me stuck for over a week now is the search function, i wanted to integrate into the page.
I use Relevanssi to replace the standard WPsearch so i can also search for authors and stuff on the rest of the website and i have a search.php specified for this search.
Now i want the search on the partners-page to "stay there" and not display the searchresults using the search.php.
I have created a searchform with a hidden field to specify the post_type "partners", a text input for the searchphrase and three select inputs for the taxonomies.
The search for the taxonimies is working just fine, but as soon as i enter a searchphrase, i get no results (which i understand, since i have deselected "partners" in the Relevanssi settings, since i don't want them displayed in my overall search results) and the layout jumps to the search.php-layout.
I tried replacing the "s" variable of the input field with my own (suche), but i don't get how i can "tell" the search to use this to display only the partners with the "suche"-value in the title.
Please help me, I'm really stuck here...
You can see all this at: