Zormi, I normally don't suggest components unless the poster asks or presents alternatives himself. In your case, I would suggest giving a good listening to the Confidence C1 IIs at about half the Diablo's price. In my humble opinion they are among the best standmounts ever, for several reasons: deep and controlled bass enough even for medium-sized rooms, a soundstage that includes height reproduction, something rare among non-tower speakers (even Vandersteen 5s and 7s, as well as highly rated standmounts such as Raidhos don't do it), and all around sound as good as anything at two or three times the price. The C1 IIs definitely don't need a crossover, just augment their already impressive bass with your RELs at about 30Hz or a bit below.
By the way, I checked the Gibraltar manual online and on page 12 it explains the way to connect to differential amplifiers such as your Krells, basically to connect the black Speakon wire to a chassis screw as was explained by others here. That's also how Nelson Pass suggest doing it with his balanced amplifiers, and he provides another set of ground posts just for that.
By the way, I checked the Gibraltar manual online and on page 12 it explains the way to connect to differential amplifiers such as your Krells, basically to connect the black Speakon wire to a chassis screw as was explained by others here. That's also how Nelson Pass suggest doing it with his balanced amplifiers, and he provides another set of ground posts just for that.