I have known this integrated quite well for the past five years with speakers even less sensitive (Magnepan and KEF) than yours and a bigger room. I have also auditioned the Lab12 pre just a few months ago in dealer’s listening room.
In a room your size you should have plenty of power to drive your SF’s to sane listening levels. I typically play music at 75-80 db’s (A-weighted) and this was absolutely no problem for the Sphinx v3 (non-Magnum). On rare occasions if I were listening to something like Tool and pushed it up to 80-84 db’s with the Sphinx, it would handle it quite nicely yet 85-87 db’s (again A-weighted), the soundstage would be effected negatively in my fully carpeted room; more so with the Maggies than the KEF’s, yet still noticeable.
With a real solid DAC the soundstage at those more sane stated listening levels was really, really nice. I had heard the Lab12 at a dealer and it too was a very nice performer. I am going the other direction than yourself with a full separates (no phono needed) set up and I did not feel compelled to purchase the Lab12 as I was looking for a significant step up in musical reproduction. As great as the Lab12 sounded, my thoughts were it would not provide enough in the upgrade path as I was seeking. So yes, with a real good DAC you will get very close I believe to your current setup give the considerations noted, with the Sphinx v3. It served me well for five years.

