On the Soundcloud player that you want to put in your post, click the Share button and copy the link
Paste the link in your post. Now highlight this link and click the Soundcloud button (it looks like this

That's it!! Here's my test player (no idea who this is, I just grabbed it from the Soundcloud site) :
I know we have a lot of ReverbNation users on here, and I am actively trying to find an easy way to embed their player as well... stay tuned.