I'm not using quotes because it would make this post more confusing... So I'll just paraphrase here.
fdhfdy asked about comparisons to the Violectric V181. Without having the V181 here for direct comparisons it is a bit hard, but here goes:
The obvious difference is that the V181 is significantly more powerful. It would be better suited for an HE-6, and would probably be better for the entire power hungry HiFiMan lineup. Also the AKG K1000 would be a good match as well, based strictly on power numbers.
As far as sound signatures, the V181 has a bit more of a warm, almost tube like character to it. Strong points include an exceedingly smooth top end and outstanding bass. The Quattro has more of a solid-state feel to it without veering too far into clinical/boring territory. High points are the open/well defined soundstage and excellent clarity.
They really are fairly different sounding amps, each with their own focus. The V181 seems more focused on overall musicality. Single ended, it can sometimes feel a bit constricted, but balanced mode takes care of that. The Quattro is more focused on inner detail and linearity. It is slightly more lit up on the top end, which sometimes comes across as more detailed and other times seems a bit grainy (often depending on the recording). When both models are used in balanced mode, the Quattro has a more open/spacious feel to it.
Both are excellent performers. I give the overall nod to the Violectric but it could really come down to matters of taste, as well as system matching. That's a big accomplishment for the little $400 price tag of the Quattro.
guido is asking about the setup: On the amp, the "remote" switch has nothing to do with volume levels. Whatever the volume knob says, that's the setting. "Remote" just enables remote control of the volume knob. By switching it to OFF, you are just telling it to ignore the signal.
Variable on the DAC does adjust the output, like you said. "Fixed" gives it a wide open output with no limitation. "Variable" uses the volume knob to trim the levels. The remote does operate the knob in this mode.
Variable mode on the DAC seems most useful in the context of a pre-amp mode - powering a (non headphone) amplifier. When using the Quattro combo, I always leave the DAC on "Fixed" mode and use the volume knob on the amp, since I'm sitting right there anyway. This means there is just one potentiometer in the chain. Remote on the amp is more of a novelty for me, but I guess some might find it useful if their chair is at a distance.
Does that clarify? I know the manual can be a bit confusing.
Regarding stacking the components: I asked JTam about heat, since both units run fairly warm to the touch. He said this was accounted for in the design, and both use components that are able to withstand these temps. The surface temp is roughly 60 degrees celsius which is about the same as the Benchmark units. Note that the older Benchmarks didn't have an "off" or "standby" mode and I don't recall them having reliability issues. As far as stacking, I've been doing it ever since I got them, without issue. I don't use any extra footers or spacing and it doesn't seem to effect anything, although it couldn't hurt either.
This is relevant to the V-200 as well?