Content loader has been deprecated in CQ 5.6.1 which might create difficulty in uploading bulk contents in CRX.
As per CQ documentation on http://dev.day.com/docs/en/cq/current/howto/website_quick.html, it is suggested to use content loader in CRX but when you will try to find content loader at http://localhost:4502/crx/loader/index.jsp, you will encounter the error: message "Content Loader have been discontinued.
Package manager is a built utility rather than import or bulk upload utility. So, it may not help.
Alternatives to upload (CSS, HTML and images) or simple content packages (without jcr:content):
1/ Use WebDav to simply move the files to CRX.
2/ Another option is to use an http client, curl for instance and the sling post servlet capabilities. see (1) for reference.