I've been designing speakers with Ralph's smaller amps (S-30 and M-60) very much in mind for years, but my speakers tend to be bigger than average (though usually not "T-1.5 big"). I do horn speakers that hopefully don't sound like horns, well at least not in the negative ways that the word "horn" can bring to mind.
In a fairly compact speaker, you might consider High Emotion Audio and Omega Loudspeakers.
At what they do well the Quad 57s are just magnificent. If you decide to do a stacked pair, contact me for a tweak suggestion.
Best of luck in your quest,
Duke
dealer/manufacturer