Also my main speakers are designed to be run full range from whatever amplifier they are connected to. I know of no speakers on the market that the manufacturer recommends they be high pass filtered to play properly.
Um, not really. But having worked as a marketing whore I can say of course the manufacturer wants you to think every speaker of theirs can play every note with perfection. No brand is going to commit sales suicide and say they must have a highpass.* Having worked as a loudspeaker engineer with a lot of friends doing that, I have to say many speakers of course cannot really handle the full spectrum at full blast. That's called "physics" ha ha. So unless the mains are pretty large (like our Focal 936, yeah no highpass really needed unless for some crazy EDM or movie special effects, at very high volume) there's more distortion.
If this distortion was a big problem, why are so many people enthralled with the sound of two way monitors?
- For one as I believe you alluded in passing, it sharply depends how loud you're playing. Us crazed metalheads aren't going to be happy, and if we need smaller mains due to space will definitely want a highpass. Someone who listens to The Kingston Trio and chamber music, eh, no problem. In which case the highpass won't matter really as you say.**
- I've never read of anyone enamored with a two-way monitor because of the bass sound. It's always about "transparency" "imaging" "depth" and so on. Many people seem to believe that a big tower can't have these qualities as well as a tinier speaker. (That hasn't been my experience, and while there is some engineering justification for that it's not something that can't be designed around IF the engineers have enough freedom. Some engineers are stuck designing to a spec thrown over the wall from sales/marketing I can testify firsthand. Heck I've sometimes been the one doing the throwing! Though I took pains to meet with the engineers and explain why certain lacks of design freedom were necessary to increase sales).
My advice about all this has become to take the most bass heavy selections you listen to and crank them as loud as you ever wood and listen especially to the bass. If it sounds fine, eh, no highpass needed. If you're not happy, try a highpass. It's unfortunate a lot of stereo equipment stupidly does not allow that option.
*excepting a few specialists-JTR, PSA/Power Sound Audio-that build models with bass purposely sacrificed for high sensitivity, in the stated assumption the system will have subwoofers.
**unless as someone alluded there is an infelicitous phase mismatch which can't be cured by the subs polarity and crossover settings.