JM Labs Electra 946 lack of high-end detail

I have a large open-plan home theater room that I could not fill with enough sound from my Boston VR-M90 mains. My (5th) sub, an SVS PB2 Plus, was up to the job, but overwhelmed the Bostons. So after reading the critiques in this forum I bought a used pair of Electra 946s. With a single Adcom 5802 they lack all high end detail. Bi-amping them with the Adcom 5802 bottom and 2 channels of an Adcom 5503 (a bright amp) brought out a lot of detail in the speakers, but they still lack the finesse and detail of the Bostons. (I like the Boston sound.) I use an Outlaw 970 pre/pro.

Any suggestions as to how to brighten up these speakers would be appreciated. My beef in partivular is with the single 5" midrange speaker and tweeter, which sound dead.

These speakers are the '80s speakers I couldn't afford back then: big stupid bass, as someone has pointed out, efficient, loud, but not refined.