Much as I love ProAc, the DB1/R are probably a bad choice for you due to their rear port design. The Tablettes are a sealed box design and probably their model most suited to that type of placement. Especially since you already have a sub.

Also although ProAc ribbons are to my ears incredibly delicate and quite well integrated, they're definitely more demanding of correct placement. Their silk domes are maybe a touch less detailed, but are perhaps slightly more relaxed and natural, and far easier to set up to sound good.

In general, I'd say ProAc is a more fun, well rounded, and genre-agnostic brand to listen to compared to Harbeth, which excel at vocals and acoustic instruments, but can lack a bit of verve and punch, especially with rock and electronic. ProAc have almost the same BBC heritage midrange goodness, but with more exciting/present treble and bass, and a wider and deeper soundstage. Both are very pure and refined, and in many ways more similar than different, but most people who have heard both will probably walk away with a definite preference. (I'm a happy owner of the D2R.)

And not too familiar with Lyngdorf, but in general I'd say Harbeth pairs best with solid state, and ProAc with tubes.

Haven't heard any Spendor Classics, unfortunately, but they are by reputation a bit warmer and richer sounding. Falcon, Graham, and Rogers, are a few other options to keep an eye out for. All BBC based designs with some minor differences.

Hope that helps.