I see that you also have exoerience with AP100 and M2. How do they compare with 990?
Both the AP100 and the M2 use the same (very popular) CirrusLogic DAC (CS4398) but sound rather different to each other. (As Wolfson is part of CirrusLogic since some years, strictly speaking the 990 has a CirrusLogic DAC as well
)
The AP100 leans a tiny bit towards the bright side so I am using it with either the NAD Viso HP50 or the Yamaha MT-220. The AP100 also has the option to do upscaling (using a CS8422 chip) which allows to feed 192KHz 24 bit into the DAC (independently of the source material). The sample rate conversion process seems to result in some slightly rolled off highs - I think that's beneficial in case of the AP100.
Nonetheless, the AP100 can still be described as being fairly neutral. Compared to the 990, it is less engaging/enthusiastic and less defined in the bass department. I would also say the 990 has a bit more sparkle (without sounding harsh at all). Overall, however, the 990 sound signature is darker so certainly pair with bright headphones. It's probably easier to find a match for the AP100. But once you have a good combo with the 990, then the 990 will outperform the AP100. Layering/separation is better on the 990. Soundstage a bit deeper (possibly also wider) on the 990.
(Note that all these impressions are influenced by the combos I am using - also consider that the HP50 generally produce a larger soundstage than the MT-220 and MSR-7.)
UI is pretty simple on both players, possibly a tiny bit nicer on the 990. But haptics are a lot better on the AP100.
As the AP100 is cheaper (and a very decent DAP) it offers better value for money. If you are mainly in for the sound quality then I would suggest the 990.
For the Shanling M2 I found that the AKG K545 are a good match (with gain setting low). Price-wise the M2 sits in-between the AP100 and the 990 - and that's probably correct when looking at sound quality. With older firmwares the M2 had a somewhat analog (but good) sound signature. With later firmwares the sound became cleaner. Now it's possible to choose the DAC filter setting in the menu. Speaking of the menu, the M2 has by far the most polished menu, translations, etc. Haptics are pretty good although navigating through folders is still easiest with the plain buttons of the AP100 in my opinion. The scroll wheel of the M2 is definitely better than of the 990. And also battery life is a lot better on the M2!
But back to sound signature. The M2 does not sound technical at all (none of the Shanling DAPs do). Instead, the sound is clean, transparent and musical at the same time. The 990 has a fuller sound (although M2 sound isn't thin either). Is the M2 as engaging as the 990? No, unfortunately not. Soundstage is more or less on the same level, but separation is slightly below the 990.
When considering the overall package then the M2 is a really, really good DAP and probably wins over the 990. When judging based on sound quality alone, then a good 990 combo can do better.
Hope I could give some useful insights
