I believe both of these companies will allow you to audition their speakers for 30 days (verify with Salk for the Song Towers - their website wasn't clear on this last time I looked).
You would have to pay shipping for the ones you returned, but in this price range, I think it'd be worth it for you to know you got the speakers you preferred.
Personally, I believe there is actually a lot of agreement on what the proper sound of a good speaker is. However, once you are talking about two very good options like this, you are getting down to the nuances. A lot depends on what music you listen to, how much you listen to live music, and in what venue you listen to live music.
I know when I had three very good speakers in my room (Song Tower Ribbon, Paradigm Sig.2, and Focal Solo6Be) I was delighted with the prospect of owning any of them. By having them together in the same room, I could detect subtle differences and decide which I preferred.
I don't think there is any other way to choose between speakers of this caliber. If they are in different rooms, the rooms are likely to be a bigger factor. I wouldn't feel comfortable listening to them in the same room at different times. You really want to go for side by side, level matched, with instant switching if you can (having two identical receivers is the most practical way I have found to do this).