You may well be expecting too much from that speaker system. To be honest Def Tech are one of my least favorite speaker companies. I'm yet to hear a speaker of theirs I could be happy listening to. They do not publish meaningful specs, and those they do publish are grossly embellished.
Lets take the bookshelves on which there is third part data.
This is the frequency response.
The ABR enclosure is severely misaligned. There is a massive bass thump at 150 Hz. Specs state the response is down to 40 Hz, but it falls like a brick at 50 Hz and is 10 db down by 40 Hz. The top end is bright, severely so.
This is a classic example of what I consider cynical design. This is a classic boom and tizz speaker. Cynical as it is designed to catch the unwary inexperienced listener.
There is not data on the center, but it is similar in concept with two ABRs, one at each end. It has 4.5" drivers that will severely decouple below tuning which I guess is higher than the 55s.
In order to avoid the thump you would have to crossover at 300 Hz which is not possible. My guess is that to avoid the decoupling causing the over excursion you describe, a crossover of at least 120 Hz is required.
Finally Def Tech subs are poorly regarded.
My gut feeling is that you are not going to be satisfied with this speaker system and will be driven to replace it with something better.