Well, for the two or three of us who are interested in this little speaker array, here are my first impressions.
AC30 clone, American Standard Tele with Lollar Special T's, so a bit darker and hotter than a normal tele, with more mids, almost a tele/p-90 hybrid sound. 11-50 strings. No pedals.
The 2x8, 2/3 closed is really impressive. Highs and lows are well-balanced, very punchy without being overly snappy even on the bridge with the tone wide open on the guitar and the amp.
Rich and crystalline highs, not at all shrill or glassy, upper mids to highs are very 3-d. I've never heard this kind of layering of the high frequencies: the mid-highs hitting first, bright and round; upper- and lower- highs a bit thicker and a bit slower in the mix, still articulate but a bit more woody.
Bass is surprisingly tight and big. Hits fast and doesn't linger. Totally beautiful breakup with a strong attack on the thicker strings. Another new sound to me, less flubby than say, a Greenback breaking up, but equally as unhinged and raunchy.
Mids and lower-mids are thicker, woody, recessed. They hit a bit later with a flatter emphasis, tend to linger a bit, not as punchy.
The 2x8 closed back definitely brings the mids and lower mids forward in the mix, a flatter, more compressed and even response. Surprisingly swampy and thick, but still retaining a crystalline, almost glittery quality in the upper mids-highs. Not as punchy as I would have expected. Almost jazzy on the neck, oozes sparks on the bridge.
So, the two chambers in parallel for a 4x8 cab, top chamber closed, bottom chamber 2/3 closed. This sounds much bigger than simply the addition of the two cabs (you hear this in 4x10's too). Incredibly rich with a rolling loose rumble in the lower mids, a very punchy bass, and upper-mids to highs which are considerably smoothed out in texture, flatter, but maintaining a good mix of crystal and wood tones. Huge sound, again, unlike any 4x10 I've heard (including my 60s Jensen/10GC mix). Surprised also that with more volume and/or harder attack, this cabinet maintains a nice balance of colors even as the sound becomes more compressed.
Feel free to ask questions, hope I represented these speakers accurately. I know there's not a lot of 4x8 cabs out there, and the ones I've seen are tiny (this is a full 24x24x12 cab).