Greetings cinnamondem, and welcome to the MODx forums!
Quick question, I am assuming that this "secondary" site is still in the CMS? Still on MODx, correct?
Using Ditto, you can pull content from anywhere in the site. For example, if you have content from a specific document you want to put on the homepage, you can create a Ditto call on the homepage, pull from that specific document (or documents) and specify the tpl (how familiar are you with Ditto at this point?) and style the content however you would like. Then on the other part of the site (i.e. in the "secondary" site), you can pull from that same document where the content resides but use a different tpl with different styling. Ditto is probably one of the most important snippets you’ll use in MODx and it’s super flexible.
One example of what I’m explaining above. On my business website, I have a blog section:
http://www.my619.com/blog
But I want the blog content to also output on the bottom of each page throughout the site but with a different styling...for example at the bottom of the homepage:
http://www.my619.com
I have 2 blogs being outputted at the very bottom that have different styling than the output of the blog in the blog section.
Hope that makes sense...please let me know if you need more info...hopefully that will spur you in the right direction.