OK, first pass review. Hardware is a 2.1 consisting of a pair of Audioengine HD3s and an Audioengine S8 sub. HD3s sit on Audioengine DS1 silicone rubber angled stands. All comments/evaluations made with magnetic grilles on the HD3s. The S8 is downward-firing and up against the wall under my desk, roughly around where my left foot would like to be. It's ported, and the port is pointing to the left (leaves me easier access to sub controls). I've got about 10 hours on the combo. Also critical to this is the fact I'm 54 with more than a few loud concerts on my ears.
Took some experimenting, but I'm in a good first spot. Sub input is taken from the line outputs of the HD3s and the bass reduction switch on the back of the HD3 master is in bass reduction mode. Crossover freq on the sub (it receives full-range input) is set to roughly 100 Hz (divisions on dial don't match stated range of the control) and level is at about 40%. HD3s are roughly 36" away from my ears, aimed directly at me (I can't see sides from where I normally sit), and subtend an angle somewhere between 50 and 60 degrees. On the stands, my ears are just about on the tweeter axis. Since I'm using a 3.5mm to RCA out of the AQ Dragonfly Black (DAC source) I've moved the master HD3 to the right side simply because cabling works better on that side (switched L/R on the RCAs into the master HD3, L/R verified by playing Supertramp's Better Days).
Music: Classical, rock from origin through 1990s "classic rock", lots of prog, smatterings of jazz. No rap, hip-hop, death metal (Deep Purple is as metal as I get) or other music whose sole point is to rattle the Bondo off cars. All music in WAV format played through Foobar2000 v1.3.14.
Volume: It'll play louder than I ever care to listen.
Frequency Response: Well, I haven't sprung for a pro analyzer Android app, but I think I've got the sub/sat merge 90% dialed in. Bumping the crossover freq from 90 Hz to 100 Hz was a major improvement and filled a hole that was there in the initial setup. Freq response now seems constant over the volume range. The HD3s are clearly aimed at treble lovers and really need the sub to balance that out (HD3s alone would be, I think, too bright). That said, I'm not hearing any sibilance or other annoying treble effects, just appropriate detail for the recording and a decent sense of "air".
Imaging/Soundstage: A strong central image for sure but good and realistic imaging (my touchstone is Cowboy Junkies Trinity Session) and if the room is there on the recording, it comes through. I'm hopeful that break-in will allow the image to extend past the subtended triangle. NINJA EDIT: Soundstaging declines quickly if your ears move behind the triangle's apex.
Overall: A whole lot better than I was expecting and something I will gladly listen to and tweak for many a year.
Disappointing niggle: The Amazon reviews are right. The volume knob (also on/off) on the master HD3 isn't glued on by much more than hope. A quick squirt of hot glue easily fixed that, but that's something that simply shouldn't happen at this price point.
What we have today is way too much pluribus and not enough unum.