I cannot speak to how they will blend with Martin-Logans, but you might look into the Paradigm Cinema Series for small interim surrounds. I have been happy with my 1050 and Cinema 90s, though I use them with a subwoofer. They are pretty cool looking, too and come in black, silver, or white.

http://www.paradigm.com/Website/SiteParadigmProduct/ParadigmModels/Cinema/Cinema_Series.html