The crossover frequency is fixed. EQ adjusts the whole range of audio as would a conventional tone control. The SUB level control adjusts only SUB. To an audio purest this is not proper, but to a bass or action movie freak this is a glorious adjustment. I know a guy who is in a special class of bass freaks. He has SUB placed in a corner (the most efficient acoustic spot for a subwoofer) with the SUB level control boosted. He also has a high frequency hearing loss and boosts the treble. To my taste his system is a screech and a thump, but he loves it. Fortunately, I don’t live there.

Goodness of sound is in the ear of the listener. Only you know what sounds “best” (to you).

I think that systems should have two audio settings: balanced for music and aggressive for movies. Many people want ‘accurate’, ‘natural’, ‘realistic’, or whatever you want to call it for music, Movies are an escape and over aggressive bass is fun in that context. A long time ago there were a few subwoofers that could be setup to make this switch automatically.

correct me if i'm wrong, but i got a feeling that the eq bass adjustments changes a bit higher bass than than the sub level. when i lower the sub level and raise the bass a little more midbass comes from the arc… but could be a placebo...

Yes, SUB handles only the low bass. Humans are silly creatures. At first rush we tend to accept frequencies in the 120Hz range as ‘bass’. Low end equipment sometimes offers a “bass boost” feature that will take advantage of this by cutting frequencies below 80-90Hz and boosting 120Hz. This lowers the overall power requirement and fools the human into accepting that the bass has been “boosted”. Arc’s EQ control will cover the 120Hz range. SUB’s Level control operates at lower frequencies. Another matter is that, if the human is blindfolded, it is difficult to walk into a room and point to SUB’s location, but it is much easier to point to the mid bass of Arc.