-Manuals and Quick Start Guides will always be found on the respective product's page, under the 'downloads' tab. Other documentation can also be found here if available, such as specifications (often found on the last page of the manual or quick start guide).
For example for the Xenyx 302 USB, the manual would be found at http://www.behringer.com/EN/Products/302USB.aspx then under the downloads tab pictured below:
TIP: Using the Search Box on the site is a quick way to get to a product page (Located on the Top Right of the website)
Then go to the section marked 'Documentation' to find downloadable PDF versions of Manuals, Quick Start Guides and further Documentation (as pictured below):