I have rebuilt Maggie 3.3rs and have used lots of different amps on them, including Rogue Magnum 120s - pretty powerful tube amps. Maggies really like to slurp good quality high power. Ultimately they are at their best actively biamped with 200-250 wpc (8 ohms) amps that double into 4 ohms.
But you can't easily biamp the 3.7i, so I would look to an amp at least 200/250 wpc into 8 ohms that doubles wattage into 4. Parasound A21 is pretty beastly and does that. I would also consider supplementing with multiple subwoofers set very low in gain.