IMO i also feel this is true. (That the m6 cannot put out strong deep bass)
......
To me this player is not even "neutral" in terms of balance in this regard.
That is totally not true if you look at these measurements.
Source: http://ohm-image.net/data/audio/rmaa-fiio-m6-24-bit (Thank you!)
Flat down to 20 Hz! Thank god! (otherwise it would be a faulty device)