I bought the NXG NX-BAS 500 based on all the glowing reviews here, but today I'm returning it. Two issues; one may be a defect (combined with poor customer support), the other is just design.
The main reason I'm returning it is because of a constant low-frequency buzz. It's not pleasant. It occurs whenever the sub is plugged in to power and turned on -- it does NOT need any input connected to do this.
When I contacted NXG support about this, I got no response. When I contacted AV House, through which I had purchased the sub on Amazon, they were very responsive, and promptly told me that NXG had contacted them after I sent my first email and informed AV House that my problem was caused by a ground loop, and that I needed to get a ground loop isolator. Amazing! They diagnosed my problem without asking me a single question!! Uh, no. They apparently didn't read my initial message either. (A) I already have a ground loop isolator. (B) This occurs when the sub isn't connected to ANYTHING (except power), so how the hell would a ground loop isolator solve the problem? Also, I moved my old Velodyne 12" down there, plugged it in, and it doesn't get any buzzing even without a GLI. So, defective sub, and it's going back.
The other problem I have is with the auto-on. Its threshold is just way too high. I often listen at low to moderate volume, not blasting it, but still enough that a little bass would be welcome. The NXG wouldn't turn on unless I turned the volume up a little more than I would like for casual evening listening. I don't have this problem with my Velodyne, it's auto-on is sensitive enough to activate even at low volumes.
So, no NXG for me; even though it sounds great, I'm reluctant to order another one if the auto-on behaves the same way; and I'm not entirely confident in their quality after the buzzing experience and the default "it's your fault" response.