I am somewhat familiar with both the 10" woofer and the coaxial driver, at least from the standpoint of having closely studied the specs for both on multiple occasions. But I don't recall seeing this particular kit before. Is it possibly a fairly new kit? I see that it is "Mk III", so there is potential for people to report experiences with one of the earlier versions, which experiences may or may not apply to the MK III.
I just tried to find the kit on Madisound, hoping not only to find it but also to find (no chance) that the kit includes the cabinets. It doesn't look like Madisound is selling this kit.
The woofer underwent some modifications in the not-very-distant past when Seas moved the manufacturing home from China. Vance Dickason put the new version through the wringer about a year and a half ago.
One of the more noteworthy facts about the woofer is that it is not optimized for use in a sealed enclosure. The Fs value is fairly low (26 Hz) and so also is the Qts value. The low Qts value is good from certain standpoints but it also means that the theoretical F3 value for the finished, sealed speaker will be somewhat high. Here, there is uncertainty because of the widely different values reported for Qts. The manufacturer's value is .27, which suggests a theoretical F3 value around 70 Hz. Dickason's measurement is higher, .38, which suggests a theoretical F3 value around 50 Hz. Either way, this is clearly a subwoofer driver meant to be used in a ported enclosure. However, with the EQ available with the Hypex amp, this will likely not be any concern.
The Qts value also affects the optimal enclosure size. Using the manufacturer's Qts and Vas values, the sealed enclosure can be as small as 1/4 cubic feet, which means that any enclosure large enough to physically contain the driver will be bigger than needed. If you use Dickason's values, the optimal sealed enclosure size is right around twice as large, i.e., .5 ft^3. The enclosure specified in the instructions are consistent with Dickason's values. I like sealed enclosures, but since you have to build the cabinet yourself anyway, I would give consideration to making the enclosure larger and making it a ported speaker with a low port tuning frequency, e.g., 25 Hz. (What I'd most likely do is follow the recommendations from the manufacturer and from Madisound for building a ported subwoofer with this driver.)
The only thing that jumps out at me as a possible concern is the unusually low crossover point at the handoff from the midrange driver to the tweeter, somewhere in the ballpark of 1.7 kHz. Anytime a tweeter this small is operated this low in frequency, there is the potential concern for tweeter distortion. The only measurements of distortion I've seen for this coaxial driver are the measurements taken by Troels Gravesen. I'm not familiar with the particulars of how he measures distortion, and with distortion measurements it is always a good idea to do comparisons with distortion measurements taken by the same person and using the same equipment, for other drivers. But Troels concluded that distortion was no concern for the tweeter if crossed over as low as 2 kHz. He worked up a passive crossover for the coaxial, using a slightly higher crossover point. Since the cabinets aren't included in the kit, one possibility that someone might consider would be to use his passive crossover, although this of course would be a very different approach making the speaker a passive speaker, in which case the design would not be complete until after having solved the crossover between the woofer and the midrange. (Evidently the crossovers in the kit are incorporated in the DSP files for the Hypex amplifier with DSP. I assume so because I didn't see any separate information about the specifics of the crossover.)
All in all this appears to be a very desirable speaker. Even though I identified a few potential deviations, I would be inclined to build it as intended, with a sealed enclosure and using the Hypex 3-way amp with DSP providing the crossover functionality and compensating for the inherent bass rolloff of the driver. For someone who doesn't prefer a self-amplified speaker, and who would have no difficulty with designing the woofer-midrange crossover, a passive approach using a ported enclosure and using Troel's midrange-tweeter crossover would also make for a very desirable speaker.
Someone who has built one of these ought to consider sending it to Amir for measurements. The distortion measurements would be especially interesting, in the 1.5 kHz to 2 kHz range in particular.
