Help for integrating WordPress in my site

Hi ! i’m running the latest version of WordPress, i plan to use it for both a blog and a news system ( the news will be in a separated category )

my main site is managed by another cms ( modx ), the articles i’ll write in the news category, in addition to be displayed in the blog managed by WordPress, will also be duplicated in the homepage of my site ( page that will remain under modx’s control

for now i think i’ll use the rss export function, to integrate those news in my homepage. Here is my question :
i also would like to display the comments on that homepage ( then without visiting WordPress itself ), if i’m not mistakening the comments can also be exported with RSS, but i also would like to enable the visitors to post comments from that homepage : is there a way to post comments to WordPress from outside it ? ( with a plug-in, a ready-to-paste php code …

( modx also includes a news management system, but as i’ll create a blog with WordPress, i’ll juste manage my news with it too )

thanks in advance