I can guess based on what the 6.2's sounded like, but it's just my opinion, so take it with a grain of salt.
The SongTower's won't sound as thin throughout the upper bass and lower mids as the Diva's do. Though the ST's voices sound more full and natural, and the tweeter will have that detailed airy sound, but without the added harshness of the Diva tweet (to my ears, of course). Finally, the bass will be tighter and quicker, but will still surprise you concerning depth and punchy impact...definitely surprised me considering the size of the drivers.
Concerning imaging, for me (in my crappy, cramped and temporary listening space), the SongTower's create a wall of sound. It depends on the recording, of course, but I am still blown away many a time with how large the sound stage is and how pinpoint the imaging is. Sometimes it literally sounds like I am listening in surround sound.
You may not hear anything that I described, but I hope you do. I really do think the midrange is the area that you'll noticed the largest change (for the good). It's been a long time since I heard the stock ST's, so this is based on my RT's. I hope that's okay. Oh, and the timbre accuracy of instruments (especially horns and stings) is leagues above the Diva's IMO. I know some people say the dome on the standard ST isn't quite as accurate throughout the timbre as the ribbon, but it's been so long that I can't honestly comment about that. All I know is that the ribbon does a superb job, especially for how much of a financial bargain the ST RT's are.
I hope that helps.
