IMO...If you currently like how your gear sounds in your room but you have never actually took the time or had an interest in measuring the room/gear to verify if what you are hearing isn't just a bunch of room anomalies "Enhancing" the sound of the musical content beyond what the original artist intended, then I think you are robbing yourself of hearing your system to its full potential.
But back to the DSP topic.
Assuming an ideal physical placement of the Speakers/Subs in the room....first and foremost (Is this even possible without measurements?), and then using only the physical controls on the Sub to "Dial it in" the rest of the way, you still wont have an ideal Phase, Time Aligned Sub with the Main speakers without the use of DSP.
Does the above matter? IME, Yes. Until I did this in my own system my feelings of the addition of Subs was that they made a nice difference only. But, after injecting DSP into the system, the Sub/Speaker integration went to unbelievable levels. I could never go back after hearing it.
You have to take the time to measure the room, view the results, make adjustments (either physically and/or via DSP FIR filter tweaks..etc), measure again, and again, and again...until you know everything is as good as it can be given the current equipment, room, budget and patience level/willingness to go through it all to find out. How important is the sound of music playing as best as possible in the room?
I feel, until someone does all of the above, then I find it odd how one can say that doing tweaks in the digital realm to a music stream via DSP before it even touches the DAC Input can be more destructive to the sound you hear compared to all the other likely room, placement issues you have lurking in the background which you are currently not aware of and how they are influencing what you are hearing.
I don't disagree that the use of DSP in a SOA system has drawbacks (especially when implemented incorrectly) but I consider any issues miniscule in the grand scheme compared to all the other benefits using DSP provides that are just not possible without it.
Tuning "By Ear" should still be included while playing with DSP but only tuning by ear on its own will only get you so far.