Congratulations on working 20 years at the same company. In recent years, that's quite an accomplishment.
Thanks for the photos and detailed description of your listening room. You've clearly thought a lot about all this.
I will limit my comments to the SCST as I haven't heard the Song3 or 3A. In short, I readily recommend them as an improvement over the Totem Hawks you now have. They will likely produce more bass than the Hawks, and the transmission line cabinet should allow flexibility in placing the speakers in your room. The larger woofer in the Song3 or 3A will probably produce more bass, at the expense of a larger cabinet. The SCST's magnesium cone mid-woofers will also produce excellent sounding detail, as will the ribbon tweeter. In the SCST that is a particularly good sounding combination. They, IMHO, should make you happy considering your goals of speaker that produce good imaging, soundstage, natural tonality, dynamics, and detail.
You mentioned you had owned SongTowers before, and loved them. Why do you no longer have them? Did you replace them with the Hawks? I'm curious about your impressions of these two speakers.
I owned SongTowers for over 9 years, and a year ago stepped up to a pair of Veracity ST speakers. (See my comment about them below.) I am also familiar with the SCST speakers, and although it was a number of years ago, I had once listened closely to the Totem Hawks. I noticed your Primaluna amp can deliver about 35-45 wpc. I have heard SongTowers driven by an AVA Ultravalve amp of 35 wpc, and it was enough to drive it adequately. I expect the SCST to be similar in that regard.
From my own experience, I couldn't agree more with you about the advantages of buying speakers from an internet direct manufacturer, especially Salk. Furthermore, Jim Salk's custom veneer finishes make my speakers better looking than any furniture I own. I spent about $175 extra for a ropey curly cherry veneer. (That cost less than FedEx shipping.) If your wife is at all reluctant about new speakers, get her involved in the veneer choice. Jim is very good at helping people to decide on those choices, so I urge you to speak with him about that.
Because you previously owned SongTowers, you are aware of their footprint and height. At 8" wide they have a similar footprint as your Hawks, but they are about 10" taller. Still that will be less of a visual change than the larger Song3 or 3A.
As far as sensitivity goes, there is no standard way that different speaker makers measure sensitivity. The SCST, Song3, Song-3A, and Totem Hawk all are said to have 88 dB sensitivity. I can believe all the Salk sensitivity measurements are done similarly, but I cannot say that Totem measures sensitivity the same way. It has been my experience that the Salk measurements of sensitivity are on the conservative side. When I have done direct comparisons of my STs to other speakers, the Salks were always more sensitive, sometimes surprisingly so, considering what their rated sensitivities were. As a result, I feel safe in guessing that the SCSTs might be more sensitive than the Hawks.
Following up on Hydro's comments -- you might want to consider the Veracity STs - sound just like the HT2-TL's, but with a much smaller footprint.
I do agree with this opinion. When I bought my Veracity STs, I did consider the SCSTs and eventually chose the VSTs over them because of their greater dynamic range and impact. The do deliver most of the what the HT2-TL can do with a smaller footprint. They are actually 1½" shorter than my STs. The only problem is they are out of abd-1's price range.