Headway works nicely with WordPress networks. For information about creating a network, see the WordPress Codex.
To use Headway in your network, install and activate it in the main site like any other theme. All sites in the network then have access to it and can be designed separately.
A domain mapping plugin (here’s an example) is required for the other WordPress sites on your network to have their own unique domains, rather than having a subdirectory or subdomain of the main domain as the URL. Headway will work properly with domain mapping activated.
PHP Parsing on Individual Sites
If the site using Headway is NOT the main site, then wp-config.php of the of either the main site (if using subdirectory install) or sub-site (if using subdomain install) must have the following variable added to the file in order for PHP to be properly parsed when used in the custom code block:
This bit of code can be added in the same way you added the code for the network setup.