I'm not sure what Alt-2 does as I have the Mac version of JRiver MC. But if it does the same thing as switching to the Playing Now view, it should do more than "bold" what's playing. It should scroll the Playing Now list so that the playing song is visible. Then show the line that's playing by displaying a bar type effect all the way across. Finally, it does highlight the text, but it's not a "bold effect". It's determined entirely by the Skin you are using.
My knowledge of this is recent because the Skin I've been using lately, Onyx, doesn't really highlight the current track very well at all. You can't really even tell it's highlighted; especially if you switch to an album view listing the tracks. So I modified the Skin (very slightly) to very clearly highlight both of those cases using a different color (sort of subtle, but very easy to see).
It think they are called HotText and SelectedText in the main.xml file of the skin. So now the file in Playing Now or in the album view both have a distinct color that makes them stand out more. Much more than a simple bold type effect.
Brian.