The hum you have picked up in your sub is probably a ground loop from the offset differential of the ground planes between the amp and the sub. These can be difficult to resolve. Might try lifting the ground on the amp and see if it goes away (or sub.)
Sometimes, the ground differential can be enough to cause such a reaction by the amp. However, my gut tells me your amp has a problem. I would pack it off to a service center for a check. NAD equipment is decent but historically, it has been known to have some issues. This series is no exception.
The NAD is certainly robust enough to drive the Totem's. Even though the speaker has a relatively low impedance in a narrow range (3.8 ohms) it is not that hard of a drive due to the speakers phase angle performance. Any decent amp should work well with these speakers.
Sometimes, the ground differential can be enough to cause such a reaction by the amp. However, my gut tells me your amp has a problem. I would pack it off to a service center for a check. NAD equipment is decent but historically, it has been known to have some issues. This series is no exception.
The NAD is certainly robust enough to drive the Totem's. Even though the speaker has a relatively low impedance in a narrow range (3.8 ohms) it is not that hard of a drive due to the speakers phase angle performance. Any decent amp should work well with these speakers.