Mark:
Thank you for your thorough and prompt reply! I did not have an exact replication of the "current home," but the choices that I did have basically self-narrowed enough to quickly discern the correct one ("Oracle in instantclient_11_2"). The funny thing here, perhaps, is that all of these options were here yesterday as I tried them one by frustrating one, and even this one did not work. However, that was before I resorted to downloading and installing this same client (Oracle 11.2), after which I did not try changing the OBDC driver setting again (simply left it on <default>). Today, changing it to that noted above allowed my first successful use of cross-connection.
I even added an Excel source and joined the tables... still no errors! I am now hopeful! Your timely intervention talked me down from the ledge just in the nick of time! Now my new concern is that my employees didn't look as relieved about that as I would have expected.... ;)