I spent some quality time with both AK240SS and AK380 + Hugo with both my pair of IEMs (Earsonics Velvet) and LCD3 (Fazor). Let me state clearly that everything is rather preliminary as I did not have time to stay with the devices for weeks and the AK380 is only burning in slowly. I have listened to various files (Redbook, HiRes and DSD 2.8/5.6). The first thing I noticed again is the excellent performance of a (semi-burned in) AK380 on its own with IEMs. I would not like to exaggerate (as the impression may change down the road), but the sound reminds me of a full-fledged home system. It is large, deep, spacious with many interesting subtleties. I must also say it is different from the AK240SS used in the same type of configuration. The AK240SS is nice and it would still be a reference player had the AK380 not be there. I am not sure on the words to use but I think, from a purely subjective point of view, the sound of AK380 as a standalone DAP is more natural while the AK240SS is a little more "artificial". Please note that "artificial" is not used with a negative connotation. It is simply more digital than the AK380. Certainly this has to do with the new chips and perhaps their implementation (leaving aside the material used - steel against duraluminium). The AK380 with certain tracks (especially DSD but sometimes with some simple CD rips) reminds me of the mood and soundstage I experience using my PS Audio Directstream DAC in full system setup.
I have then tried AK380 and AK240SS paired with my Hugo via optical cable with both IEMs and LCD 3. I must say I am a big fan of Hugo sound and I have been using it with my home system before getting the PS Audio Directstream. However, when AK380 is paired with Hugo, I find that it loses its "magic". More precisely, if I were to use IEMs with AK380+Hugo I would find the bass deep but a bit more bloated than using the AK380 alone. In addition, albeit the Hugo signature sound is retained, the subtleties noted with the AK380 on its own are no longer there. Note that this does not mean that the Hugo sound is not good. To me, it only means that perhaps there are less synergies between AK380 and Hugo. When I used the AK380 + Hugo with LCD 3 (there is no other way to use LCD with AK380 now as the power may not be sufficient) I still find the combo nice but it does not strike me as very different from the one I have been listening to for a couple of months comprising AK120 Titan + Hugo. It is slightly better, but not worlds apart.
The story is rather different when I paired AK240SS with Hugo and used both IEMs and LCD 3. If I had to choose one DAP to be used with my IEMs, my preference would certainly go for AK380. The AK240SS is excellent on many respects (especially naturalness of the presentation) but I cannot stop thinking about that lack of space I get when I compare A/B AK380/AK240SS. When added to Hugo, though, the AK240SS improves (ever so slightly but in a nice manner). For example the bass that were not as tight as with AK380 + Hugo are nice, lush, full and deep with the AK240SS + Hugo. The same feeling of completeness applies to mids and trebles. Somehow, AK240SS + Hugo is a better marriage than AK380 + Hugo. This feeling is perceived strongly when LCD 3 are used instead of IEMs.
One quick note on the hardware: AK380 is rather big (especially in comparison with AK240/AK240SS). However, it is light and easy to carry around. In addition, especially the units I have tried (with 1.0 FW) are really snappy. a full 128GB card with music in various formats, is read within 1 minute. In addition the artwork is displayed more quickly with no obvious delay (which somehow occurs on previous models).
Assuming that the little disagreement between AK380 + Hugo remains even after a full burn-in of the AK380, I believe it would be interesting to check carefully what is the performance of the AK380 + the AK external amp with a full-fledged headphone. So far I have not been able to find one to try but I will report some findings if I happen to have the luck to spend some time with it.