Why not purchase the same brand of subwoofer as your tower speakers that are already designed to be integrated with your tower speakers for best performance?
That seems to be how most manufacturers work today. Already doing all of the testing so your tower speakers and subwoofer work together as a single unit?
And I agree that everyone wanting a "small" subwoofer enclosure instead of the proper size enclosure is doing themselves a diservice.
If your main goal is sound quality, then form follows function. That doesn't mean an 8 inch subwoofer cannot perform well. In the proper
enclosure it can. What I would recommend is if you can afford 2 subwoofers you will find that is probably the sound you are looking for that a single subwoofer
can rarely perform.
I think if you have a good quality signal, even digital with Toslink fiber optics for that "True" 5.1 surround sound experience you really shouldn't need a DSP in the first place.
I don't modify my sound signature allowing the music to play as best and close to how it was originally recorded. Is a 2 millisecond delay
between speakers even audible? I don't use a DSP and to keep latency or time delay at a minimum I just have my subwoofer spaced evenly, but close to my tower speakers. Preferring to come outward from a corner in my living room instead of placing my speakers flush with a wall. This allows my subwoofer to be placed just behind the tv (which is on a stand and not on the wall) and only 2 feet from each of my tower speakers. And my tower speakers facing the opposite wall at a 45 degree angle - no transient soundwaves to bounce back and cancel soundwaves from the speakers. They don't get reflected back towards your speakers. You should try it if you have the space. It really works (and yes fills the entire house with quality sound. Why I configure my system that way). Peace.