I stand corrected. The material isn't, per say "fabric", but it is very easy to cut. I simply drilled holes from underneath around the perimeter to use as a guide, then cut through it with tin snips.
Here are the pics of my finished product.
I just made holes for the bass from the sub to come through, and it made a huge difference.
How I did it was
1.) Bought these grills off eBay BLACK DELUXE REPLACEMENT 6x9 SPEAKER GRILL PAIR | eBay
2.) Drilled the holes from the bottom around the perimeter using a 1/4" drill bit
3.) Lined the grills up with the LATCH mounts and the holes I drilled out
4.) Drilled 1/8" holes through the screw holes in the speaker grills
5.) Cut the black felt to wrap around the grills
6.) Sprayed the grills lightly with 3M spray adhesive
7.) Wrapped the grills with the felt.
8.) Mounted the grills from underneath using #10 x 1/2" sheet metal screws and 1/4" washers.