domain mapping, A-record v CNAME, GoDaddy

Long story short: i can’t get domain mapping to work. After following the install guides, I have taken to randomly screwing around with A-records and CNAMES for my main multisite, call it rb.com, and one of the several sites i would like to map to it, say, cb.com. I set up a directory called cb in the rb.com site, and have the cb.com A-record pointing to the static ip for rb.com. Kept getting 403 and no access to root errors. So i tried also setting a CNAME. Same errors. I can’t get to it using the cb.com url, nor thru the WP menus from rb.com. Is there a clear, step-by-step document anywhere stating what to do, in what order, to map other domains to a WP multi-site? Most of the documents reference super admin, which seems not to exist on my install. And, most of the work really would seem to be at my service provider, which is GoDaddy, although i can’t figure out at all where WP decides what directory to go to when the “external” (mapped) domain is requested. And the examples tend to be carelessly referenced, intermixing sub-domain and mapped domain examples.