The Bryston 5B-ST has an actual power output of about 150 wpc (about 30 wpc higher than the rated output), which should be enough to adequately drive the Maggies, PROVIDED they are in a small to medium sized room, and you don't try to drive them to very high volume levels. If either of the two conditions I just mentioned occur, then 150 wpc could be too little to do justice to the Maggies.
I'm curious if you intend to use the 5B-ST in its full 3-channel configuration. Since the 5B-ST has 3 fully discrete amplifier modules, each with its own transformer, you won't get any benefits of a large shared power supply which can be beneficial if you intend to drive only the left and right front speakers.