It would seem to me that you have two issues here; perhaps they are related, but it is also quite possible that they are not related. The first thing I would do is isolate the two conditions (protection circuit and hum) by completely removing the sub from the system. Secondly, I wouldn't consider it a forgone conclusion that the amp is damaged just because the protection circuit is activated, especially if you powered off shortly afterwards.
I have the 375 also, and I think it to be a fine amp capable of driving just about any speaker. I find it puzzling that some would suggest it isn't robust enough. That just doesn't seem to be a rational suggestion; clearly information is missing somewhere.
When the sub is completely disconnected from the amp (all wires and interconnects removed), is the protection circuit still activating? If so, the next item to examine is the connections to the speakers. The 375 has two sets of speaker posts (A and B). Are you using only one set (A or B) of speaker posts or are you using both speaker posts (A and B)? If using both, what speakers are the second set of posts connected to?
On the back of the amp, I prefer the soft clipping be turned off but this is just a matter of preference. Also, the amp should be set to stereo. One more idea: there is a fuse with access from the back of the amp. You may want to pull the fuse out and take a peek at it. Perhaps the fuse is blown. Keep in mind a blown fuse is a symptom, not the cause. You will still need to trouble shoot to determine what caused the fuse to blow.
If the protection circuit is not activated when the sub is completely disconnected, then there is a problem with the way the sub is hooked up and connected to the amp.
We can give more specific help once we have a better idea how the amp performs independently and without any sub connected.
I have the 375 also, and I think it to be a fine amp capable of driving just about any speaker. I find it puzzling that some would suggest it isn't robust enough. That just doesn't seem to be a rational suggestion; clearly information is missing somewhere.
When the sub is completely disconnected from the amp (all wires and interconnects removed), is the protection circuit still activating? If so, the next item to examine is the connections to the speakers. The 375 has two sets of speaker posts (A and B). Are you using only one set (A or B) of speaker posts or are you using both speaker posts (A and B)? If using both, what speakers are the second set of posts connected to?
On the back of the amp, I prefer the soft clipping be turned off but this is just a matter of preference. Also, the amp should be set to stereo. One more idea: there is a fuse with access from the back of the amp. You may want to pull the fuse out and take a peek at it. Perhaps the fuse is blown. Keep in mind a blown fuse is a symptom, not the cause. You will still need to trouble shoot to determine what caused the fuse to blow.
If the protection circuit is not activated when the sub is completely disconnected, then there is a problem with the way the sub is hooked up and connected to the amp.
We can give more specific help once we have a better idea how the amp performs independently and without any sub connected.