Can't you ask a granite fabricator to cut the same granite slab into the shape of your new island. I'm guessing once you have the slab removed you can unscrew the cabinets that make the angle, have the counter top recut and replaced and then you are back in business!.

It is not that easy to remove and recut an existing granite piece after it's installed, especially when there are cut outs in it, which create weak spots. This one appears to have a cook top in it.

I agree with mrstinylady, I would suggest a completely different material on the island top. Something with a contrast to your existing rather than trying to match. A quartz may be nice or a granite with some movement and interest and on the lighter side.

I'll post some pictures when I get back to my computer.

I know you asked for advice re:stone and shape but I have to tell you that my friend has almost this same kitchen and she has a playful, cherrry red wall with this combination and it looks very clean and fresh.

How about a butcher block as the island's top.

You mentioned only changing the countertop. Can it be brought out more into the room? Also this image has an example of a nice countertop to mix with your black.

I wouldn't even replace the island, I would paint/stain it a contrasting yet complimentary color based on the rest of the room. Then, a countertop like this to just , the island , http://www.ciot.com/quebec/en/habitat/tiles/granite/classic/kashmir-white-granite/index.sn Paint the walls a neutral tan color, there are many to choose from. Add a runner rug in place of the small rug in front of the sink. And this just depends on taste........... A more subdued, yet still transitional......
http://www.arearugsusa.net/product-logos/originals/45279_2.jpg A little more bold, but still considered to be classic........ http://www.overstock.com/Home-Garden/Hand-hooked-Botanical-Black-Wool-Runner-26-x-6/3504508/product.html And if it is a possibility, add crown moulding too!

Changing the shape of your island is a great idea. Your current island emphasizes your kitchen's angles. In terms of color--contrast would be nice, so consider a darker stain. For the counter, "frosty carrera" by ceasarstone would give you the look of marble. Replace, the wood knobs with satin nickel, or pewterish hardware. Remember, hardware is jewelry for your cabinets. Lastly, the space above your cabinets looks cluttered. Consider edititing a bit or up lighting. Have fun!

Can you post a floor plan of the entire room and adjoining rooms?

WOW Lkristine ! Great website!
http://www.ciot.com/quebec/en/habitat/tiles/granite/classic/kashmir-white-granite/index.sn

If you want to go for a butcher block countertop this is a good place. http://chopbloccuttingboards.com/butcher-block-countertops/

Make center island so you can put counter stools there. Make the top a soft color like pic on your comments. Pick up some of the black with other colors. Take a color from island granite . For walls. Another thing remove all clutter above cabinets. Not needed. Put lighting up there like rope lite.