I assume that you want to be able to listen to everything and when you hear a track you like, you can mark it and create "best songs" list.

Not really possible directly at the moment. However, you can mark the tracks when you like them no problem. Then:

1) From emplode added the marked field to your entire track listing.
2) Sort by marked tracks by clicking on the header.
3) Then create a new playlist called "faves" or something.
4) Drag all the marked tracks into it.

If you put a ( at the front of faves i.e. (faves) it will appear first in the playlists on the empeg. However it will still appear under "F" in emplode.

I'm writing this without emplode in front of me so I'm kinda writing blind but I think you'll know what I mean. And obviously you can't do it on the fly in the car but I take my empeg in every night and hook it up so it's pretty easy for me.