Looking at the Salk website the 1801-TL has the Hiquphon OW1 tweeter and the SongTowers have the Hiquphon OW2 tweeter. I'm not sure of the differences between the two tweeters.
Bill
Oops - I see you already mentioned a change from dome to ribbon. In any case I switched from standard song tower to supercharged. Not exactly the same scenario here, but should be close. The benefit to me was a little better in the high frequency detail, bass was more noticeable. I did not do side-by-side comparison. For you, you'll get the benefit of the ribbon tweeter (however some do prefer the dome), and two larger mid woofers. I suspect bass will be more forceful in your room - perhaps less strain on them too.