Adobe Portfolio domain name question (or confusion)

I have two website names one for my personal stuff  and one for my street photography. For the sake of simplicity stuff.com and street.com. Stuff.com was created prior to the multiple site option was introduced. I created 3 A Records (*,@,www) over on the NameCheap dashboard. Everything works perfectly.

Now I want to add street.com but I'm a bit stymied. All I can successfully publish is street.myportfolio.com.

I already had purchased a number of domain names from NameCheap long before Adobe's Creative Cloud services was created. Attempting to use the Adobe Portfolio interface to purchase a domain name doesn't work for me. I do have a basic understanding of DNS Records (probably enough to be dangerous). The original A Records point to the DNS address provided by Adobe. Is the new site actually a subdomain? If so I'm not quite sure how of the proper way to Alias(?) the new site. Do I need to change the original A Records? Do I need to add Cnames to the original domain?

Can someone provide me some assistance?

TIA
--Rich