What about a burgundy (merlot) pair instead of the black? You have the black covered with the captoes you already own. I just picked up a pair of merlot McAllister and find that they go with everything. You can wear them with your gray and charcoal suits and go with the walnut for the navy. Merlot and burgundy are available in other AE models as well. I also have a pair of walnut McAllister and I love them and they look great with navy. I will warn you however that they are a little "flashy". If your office environment is more conservative you may want to keep that in mind. Mine is not and I can get away with it and get comments all the time on the walnut.
I am in a similar situation.
Purchased a pair of McAllisters in walnut recently. Then I saw the merlot color in person and it's quite sexy.
Now I cannot decide on which color; merlot that is versatile with other colors or walnut that is only good with practically navy and grey.
Is it okay to wear merlot with black pants?