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).

Try S/PDIF and pray for sound. :)

If you are NOT using USB try different S/PDIF source. That it's something wrong with ZERO ... I guess.

Yes it's the most important. I changed the setpoint of the LPF filter and in my ZERO I also changed the four decoupling caps right in front of the LPF filter. Also the OAs were changed to OPA627.

Mine is also heavily modded (more than the one mentioned above), total cost is less than 300$. The price is lower since I'm not placebo lover so I didn't changed IEC or RCA connectors or others. In my experience ZERO can beat many DAC/AMPs up to ~500 to 600$.

It's normal with cheap potentiometers like one in ZERO.

Yeah, it's the same. ZERO can be modded to 24/96 USB with I2S: TE7022 module. This module is very good, requires little modding and is great combination with AK DAC (when I2S output used). ZERO has one advantage: it can be used as preamplifier. If you don't need it than AK will be better for...

In my experience there's not much that can beat modded ZERO in the ~500$ price range. Old headamp and USB is nothing special, but DAC is great. Great DAC is also HRT Music Streamer II (no modding potential here), or a heavily modded AK4396 DAC - just search eBay for "24BIT 192KHZ CS8416 +...