No, these are not the same devices the feds helped consumers purchase. Those where strictly for Over-The-Air (OTA) digital transmissions. The devices you receive from your cable company are tuned for and activated by your cable company. While you *may* be able to purchase a digital adapter, it's entirely up to your cable company to decide whether or not to activate it. If they decide they won't activate it, you just bought a new paper weight.
If you need more than the two digital adapters that your cable company provides, I'd probably start a dialog with the cable company. Let them know you are unhappy with the need to rent additional adapters and would like to instead purchase one (or more). They may work with you, they may not.
Sorry, Wolf, I meant to select your answer as best. (It was unclear exactly whether the "best answer" click referred to the answer above or below it.) Thank you for your help. It allowed me to decide to purchase my own equipment and stream thru my computer, sidestepping the monthly charges and extra equipment required by the cable company. Our house is hardwired.