puppy-t,
nothing wrong with the subwoofer- i believe the issue is that your main speakers have very extended bass output- down to 35 hz less 3db. This is the "F3" frequency (where bass response is 3 decibel down from the rest of the audio range). The "F3" frequency is typically the starting point for subwoofer crossover setting.
Setting the crossover so low means that the sub will not have much contribution - few musical passages have output this low.
If the crossover is set higher, then you will have lots of issues because the signals will overlap, not be in ideal phase or timing, etc.
I had this same problem and despite the best integration tuning with measurements, positioning, crossover and phase adjustments, ARC room correction- in the end I could not get the system to sound great most of the time and I got rid of the subwoofers.
Room correction software will adjust the frequencies but not the phase issues.
The only option to get this to work was to filter the bass from my main speakers with an additional crossover- say cutting them at 80 Hz for example instead of letting them run full range. This might be a option for you but I chose not to.
My successful option was to run a more powerful amp to drive bass through my main speakers. Yours is certainly up to the task.
The other option is for you to set the crossover on the sub to 35 hz and be prepared to enjoy the occasional really deep bass notes.
peace.