What I do is, go to the directory in the file-browser, then a long-select gives me the option to "Current Playlist" and "Insert". Then, if "repeat" is on, it will repeat that...
One way you're confused is saying "not working with playlists" - Rockbox *ALWAYS* is playing a playlist. When you play a song - you're creating a one song playlist. When you do a long-select on a directory to play that directory - you're creating a playlist from that directory. No exceptions - there is ALWAYS a playlist that you're playing. Even if you don't save it or name it. So, your real question is 2 parts: (a), how do you make a playlist from the current directory, and (b), how do you make that playlist repeat.