Unless you are using a tube amp with output transformers you really don't need the adapter box, unless you are using a monster amp. So the adapter box drops the impedance and provides protection. Since the resistors are in the signal path they will heat up. Now some people say that the resistance of the resistor changes with temperature and this could be detectable by ear. But this may also depend on the type of resistor.
Yes, I got the adapter to protect my tube amp investment - 40wpc Tube monaural amps w/output transformers. And I really want to avoid a 2-cent set of resistors from mucking it up! My HE-6 will be leashed to the Monster Receiver direct via taps.