1) Many amps or preamps have built in filtering already. An HPF3 may duplicate in some way what you already have, but could give your more flexibility and control of what's going on down there. That's your call as to if you're finding that your cabs are creating trouble in the room and/or are experiencing more than necessary for what you're actually hearing.
2) The fEARful is really designed to be flat down into the 40hz range. The fdeck set at its rock bottom is at 35hz. Many cabs will tell you the useable low frequency is in the 40's but it rarely is, unless you count -10db or even more attenuation to be terribly useable, and/or in comparison to the low-mid hump most have baked in. So, for those of use who DO like deep lows, we can get them...but as with any new 'palate' for an artist to work with, its nice to have some control over that range, so you can paint it however you want. I even have the optional port shelf extension which gives me some extra sensitivity in the deep lows at the expense of some above that.
3) Before I switched to the Monique preamp it wasn't a problem. The Kern I used before can have the bass controls pushed but never get the level of speaker excursion or subsonics in the room. Previous to that, any of the standard 'heads' or micros I've used don't produce deep deep content by design. Jule made a design decision that says 'more is more' meaning rather than filter, the output on his unit reaches as low as the signal that feeds it, then the user and/or engineer can figure out what the do and don't want to hear with it. Its not a problem for most people, but I boost lows at my bass and at the Monique before hitting my power amp...and I can now fine tune the amount of 'deep reach' that boost has. Again, if you've got a standard production cab it ain't making those sounds although you'll be reaching mechanical limits of the speakers well before you get to the kind of volume I use on stage.
