Wattage ratings alone do not tell the whole story. However, your Marantz at 120 watts is not "way too small" for the Maggie 1.6s. Generally, the Maggies need an amp the will drive a 4 ohm load. The best values would be a solid state amp like the Marsh A-400 or BAT VK200. Tubes will work but you need at least 100 watts.
While the Maggies will work in a H/T setup, they may not be the best choice for a "smaller room." Not only will they visually dominate a smaller room, the speakers sound best when they are at least 3' from the front wall with the listening position at least 6' away. More importantly, is that the Maggies project a small sweet spot and sound best in a high quality 2-channel setup; the Maggies forte' is soundstaging. Consider that there will be a discontinuity between the center channel and the Maggies. Consider, also, that in a H/T setup, a conventional cone speaker will sound more dynamic and will resolve more low level details at lower volume levels.