[mrconfuse]

Some players like (Astell & Kern) have replay gain built into the player. Do you still need to have your files tagged for replay gain to have an effect? I know on a computer the replaygain is ignored unless the file itself has been tag with replay gain

I notice that Cowon has this called A.I audio which also balances audio but it doesn't require you having to tag each audio file for it to work.

 

[Roseval]

Basically replaygain is normalizing the loudness, you have to analyze the file first then a tag is written e.g. -7dB.
Maybe Cowon is doing it on the fly.
What they say about AI is most of all a bit unclear to me.

Some songs' volume is too high or low. The PLENUE 2 Mark ll's AI function handles these situations with ease.
AI Volume continuously normalizes volume levels of sound files played more than once. You no longer have to adjust the volume of each of your songs.
http://www.cowonglobal.com/product/PLENUE2MK2/

How have you established Cowon is not using a tag?