Yes, it is used for protection and it needs some force to pull it out, so try harder.  

HumanSaurusRex: in the 2010 the ZERO was certainly better than Dacmagic. But I think there were some updates on DACmagic since that time, but there were also quite big audible differences in ZERO in that time. jocar37: ZERO works even with all inputs connected, so I recommend trying optical...

I don't quite uderstand what's the problem with switch replacement - you just unsrew two screws, remove the black shrink-tube (= cut it open) and replace the switch for new one. About the recommendation: on the same level as ZERO there is Audinst HUD-mx1 for example; better choices than...

Fix it by replacing the power switch with new one...    If you feel like replacing ZERO for something better then start with something more expensive than 200$.

No, the "new" 09 amp is the same. My new amp is this: http://amarokcz.wz.cz/BUFFE.htm

Yes, 2Vrms is enough, but here the output will be 4Vrms: output from headphone amplifier is 8Vrms, output impedance of regulated LINE OUT is the same as input impedance of connected amplifier so the output voltage will be 4Vrms (resistive voltage divider: input 8V ant two resistors, both 10k).

Since typical amplifier (stand-alone) has input impedance of 10kohm the output will be "only" 4Vrms.  Yes it's bad for signal, but it's like having preamplifier which is quite common and not supposed to be bad...

I have schematic so I'm 100% sure. The signal path of regulated LINE OUT is following: DAC => headphone amp => headphone jack (it serves as switch: when there are no headphones plugged the output is wsitched towards line out connectors) => serial resistors (10k) => RCA connectors. Second "proof"...

The hottest place should be near the vents on the right side of the case. My normal temperature is ~15°C above the room temperature. Once I had another ZERO that was very hot becuse of the transformer. But it was the old ZERO (see first post).

Well I said that because it's true in some cases: LINE OUT can be either amped or not. You can switch between these two modes using one button on front panel. So you can connect M3 to RCA LINE OUT (asd preffereably use fixed - unamped - output) and also connect speakers to either 1/4 jack or RCA...

Not sure if we understand each other. Fixed LINE isn't amped. Regulated LINE is amped.   M3 has volume control so you can just use ZERO switched on fixed output LINE as DAC without volume control. ...or no?

Yes, the regulated LINE OUT is amped the same way as headphone out.

ZERO has one LINE OUT, but it is switchable between: (1) fixed output; and (2) regulated output (regulation via volume control on front panel).