[Crazykiwi]

I just picked up a Matrix M-Stage for use primarily with some HD650's.  Any thoughts on the ideal 'gain' to set it at?  I can hear a difference from listening straight out of the Fiiio E18 DAC.  The sound is less congested and the veil lifts a little.  However I am getting some slightly boomy bass at times.  It feels a bit too much.  Is this normal for the M-Stage?  Can the gain help with this at all.
 
My options are: 0, 10, 18, 20db.
 
Also please consider I may run the 225i or k550 if there is any benefit to that.  Would the gain need to be adjusted each time and to what level?  Also could this amp harm my lower impedance headphones? This is my first amp with kick.

 

[TwelveTrains]

Whatever gain gives you a normal listening level around noon on the dial, probably 0db or 10db. 

 

[Crazykiwi]

Great, looks like you are right either 0db or 10db.  I'll try 0db for a bit and see how it sounds.  Thanks for the help!