SoundCloud provides an API which will give you all the information you need. Though I've never used it, there's a PHP SDK which might be useful to you.
From there, if you want to get the stream information (that is, the same tracks you get when, while logged in, you see when you go to soundcloud.com/stream), you'll need to do authentication first. Information about that is here: http://developers.soundcloud.com/docs/api/reference#connect
After that, make a request to one of the /me/activities endpoints described here http://developers.soundcloud.com/docs/api/reference#activities and you'll get some information about the tracks. A track will contain tag_list
which you can then parse into individual tags and create a playlist or do whatever you want.