Do you get hissing / white noise with your M6?

A little on my SL. My friend's old SP hiss very noticeably like the old iPods.

Do you think EQing would help, or even freezing it?

This issue has been discussed in depth in various other threads.

Applying an EQ process to the audio will not mitigate or fix it. In particular, do not use the spatialiser as that appears to increase the volume of the white noise.

The only method I know of reducing the white noise is to simply use a portable amplifier to clean up the signal. Perhaps using an impedance adaptor also works, but will make your music softer requiring you to turn it up more, hence less battery life.