You can not connect a microphone directly to the iriver H10, it has not any mic input and the only line in is in the cradle and it is not too stealthy
not to talk you only can record in mp3 (even with rockbox it only works from the internal Mic at this point, the builds are 'experimental' so far)
The only way would be with a cable with a line-in in one side and that propietary iriver plug on the other side (but just to mp3)
If you like iriver and want to stealth go for an h120/h140, these ones have all you want and more