I would say they are already tied into the den brick but not the kitchen. Do a light greywash on them, then step back and see if you like it. if not, add more grey wash. Keep doing this little by little until you like it.

If you don't end up liking it you can always cover with wood.

I think you are going to end up preferring a fully painted brick perhaps the grey you have above cabinets or even a darker gray pulled from the vein in your new granite.

A black paint would tie into the black in the bricks and to your hardware/appliances and tile accents.

Sorry no suggestions, but it looks beautiful, good luck and congrats.

The brick in the den is heavy, so I would not put it on the island. It's too much. Covering with wood would be a good choice.

No, I would not put the brick on your island. There is enough separation of space from your den. It looks like a BBQ pit. I would wrap it in wood panels and paint them a color to contrast to with your beautiful white cabinets.

Paint it white

Your floors and wall color already give you enough visual flow between the kitchen and family room.

Right now the brick island is the focal point of the kitchen, I'd rather it be your pretty counters. The easiest and cheapest solution would be to paint or whitewash to match the cabinets.

IMO remove the brick from the island it does not belong there but then neither does the fancy tile work behind the stove work IMO. Right now if all you can mange is paint the brick the same as the cabinets.

Whatever the detail is, above the upper cabinets, is exactly what I would do with the island. <3 Same materials, color, trim (but create a nice hefty baseboard on the island), etc.

Edited to add: And then, to tie the kitchen into the adjacent room, I'd use the same detail above the cabinets/newly applied to island, and do the same thing on the back wall of the built-ins (assuming you will keep them open for shelving and not cover them with cabinet doors), as well as above the door to the outside. There may be other places in the den to add the paneling (?), like behind a TV or something, but we can't see the other walls of that room, so I'm not sure where else y'all could add it. ;-)

so what did your do with the brick island?