Hi ClayB,
What NAD is doing with their fancy "PowerDrive" description is essentially admitting that the protection circuitry is always operating and will current-limit the NAD's output (hence reduce the power output) if it senses too low an impedance, or excessive current flow. When protection circuitry is too over-protective, as it is in some brands (Onkyo, for one), it may severely limit the receiver's power output into lower impedances.
As JohnK points out, one way of "tricking" the protection circuitry on some units is to always leave the impedance switch on the receiver (if there is one) set to 8 ohms.
On the other hand, NAD amps and receivers in the past have not had any problems driving lower impedances.
Regards,
Alan
