I used a thin knife blade. Slide it between the grill and the edge of the cabinet near a corner and turn the blade toward the grill and carefully pull up until it stops. Repeat on each corner until you can remove the grill with your hand. The grill isn't attached with any clips or screws.
Get yourself a pair of needle nose pliers and one of those non standard larger sized paper clips. Unfold the paperclip until its just a straight piece of metal and then look at the holes on the Bose metal grill. Roughly estimate a semi-circle going through one of the speaker grill holes, looping under the grill and coming out another hole from the underside about 3 to 5 holes away and then take your pliers and bend one end of your paperclip to that estimate. Your paperclip should be straight with a loop at one end that looks like a fish hook. Loop the fish hook side into a grill hole about a third of the way in from one of the left or right sides of the speaker, not the top or bottom, then rotate it so the end loops and comes out from the bottom and out another grill hole. Grab the end of the paperclip that loops out from the underside with the needle nose pliers and gently pull it through with half the clip going in and the other half coming out with a loop in the middle. The paper clip should look like a horseshoe with the ends of the horseshoe sticking straight up from each of the two grill holes. Pinch the two ends of your horseshoe paperclip together with your fingers, then grab the ends with the needle nose pliers and firmly, but cautiously, yank straight up. Half the grill should pop right up and out. Pull the paper clip out, rinse repeat on the other end, and voila~, grill is out with no damage to either the grill or the plastic sides of the Bose cabinets.