I just spotted this post from Acoustic Research Hong Kong's facebook page, it is an official reply:
[COLOR=141823]M20 is the simplified version of M2. There will only be one 3.5mm output instead of two. The DAC will be BurrBrown PCM5242. There will still be a dual crystal oscillator configuration for native multiple sample rate support so there is no need to fa[/COLOR][COLOR=141823]ll back to lousy low precision "upsampling". High precision digital volume control will be implemented instead of the ALPS analogue volume control. There will be 32GB of internal memory. Still, MicroSDXC slot allows storage upgrade. File formats support will be identical to M2. Gapless album support will be available to M20 at launch.
Comparing M2 and M20, M2 delivers much warmer and more detailed sound. Still, we are sure that M20 will give some hard time for the competitions to match. Also, the maximum output of M20 will be 2.1V RMS. It works better with low to medium impedance earphones.
For M2 users, worry not about the gapless album support. The gapless support will soon be available through firmware upgrade very soon. Also, there will be a new accessory, impedance adapter for M2, will be available for improving the matching for low impedance in-ear earphones.[/COLOR]
[COLOR=141823]Source: [/COLOR]
https://www.facebook.com/AcousticResearchHK/