Images uploading to wrong directory after changing to multisite

Check the value of the ms_files_rewriting option in the site_options table.

If ms_files_rewriting is disabled, then WordPress will automatically append /sites/number to that Upload Path value for the subsites.

This setting should be disabled by default for any Multisite networks created after WordPress 3.5. It should only be enabled for older networks.

If that setting is properly disabled, then simply remove the extra /sites/6 from your Upload Path. WordPress will add it in for you.

Basically, WordPress 3.5 changed how uploads were stored for multisites, and how those upload path options works. The setting exists to differentiate between the two different configurations. The /blogs.dir/ thing is the old way. The new way is simply to put them in /wp-content/uploads/sites/number instead, and link directly to their URLs. No more RewriteRules for files needed.