Yes the PM-3 is quite more detailed than the H6 and the bass are more tighter, but that's all. Between the brighter sound of H6 and the veiled one of PM-3, that depends on your preference and the musical style you listen to. And you forgot, the most important quality of the H6, his soundstage...

  Could you please test the M-10 plugged with 6.35mm jack on an electrodynamic amp with a 6.35 -> rca cable or an 6.35->3.25mm jack one ? (see my post two days ago) Just to share your impression of the sound with this unit between the DAC and the M-10. I'm curious to know what you will think...

Yes I know, but except if you have a very powerfull and warm sound factor DAC, It will sound flat, no infra bass, dirty basses and low mediums, and no medium.... It's like the FIIO portable amps which is plugged on powerless dap or smartphone output, except the amp is before the Kingsound M-10...

Yes M-10 is a good converter, not a good amp. It's why you must combine the M-10 with a preamp.   I edited my last post with an image which explains the way to exploit the true potiential of the KS-H3. Soon I will receive my AKG K551 ear pads which have the same diameter, except the smaller...

EDIT : The part with K701 earpads has been removed because velvet and electrostatic are not a good mid someone told me. I'm awaiting for AKG K550 earpads which are in leather. I will update this after giving a try. How I proceed ? The M-10 is the worst amp I have ever seen, it does not...