Oi, ok, without knowing anything about the system you have and assuming the ADL is an amplifier for the headphones only acting as a pass-through to the amplified speakers, for maximum out put I would use these general procedures:

1. Using the headphones plugged in to the Amplifier powering the speakers, with the volume set at 50% or less, increase the volume coming from the PC until you hear the sound start to distort (clipping, like when a violin starts to sound like an electric guitar from a metal band). Turn it back to when the distortion stops and note at what level this occurs. You now have found the maximum level the input stage of the external amp can take. But wait, you're not done because different recordings all have their own levels, so use about 15% less to be in the ballpark for a general setting. (you can use keyboard or mouse to control volume at any setting below the value you ended up with)

Still with me? Ok.

1. Now that you have a clean input setting for the speaker amp you can now find where the speaker amp starts it's own overdrive, again looking for when Itzhak Perlman starts to sound like Mötorhead to tell you when you reached maximum ooomf from the amp and again turn it back 10 - 15% to allow for level differences. (with the PC set at the max level found in step 1 you can also attenuate the volume on the speaker, which is my preferred method as it is the last link in the chain. Many speakers with built in amplification also have remotes so you can control the volume from anywhere in the room, the idea being that you have maximum power available at all times should that be what you want).

Funny the 2 looks exactly the same as one, I wonder how that happens. Ok, if for some reason you start listening to a lot of Gangster Rap (as if) you may have to reduce levels even more because the lower bass frequencies eat up more juice than a Truck at full throttle going up a steep mountain in first gear.

It doesn't much matter where you control the volume from, so long as you stay below the max levels found, but to find max earblasting levels use the procedure.

Gold? Yes please! Ok, corrosion/oxidation is the biggest inhibitor for clean signal flow and gold plating is one of the best methods ensuring there is no corrosion. That being said, there is no reason chrome or nickel plated plugs can't provide excellent conductivity, the question is for how long. On the other hand, gold is relatively soft and would wear off faster still allowing for oxidation to form on connectors. Plug it in and leave it connected? Use gold. Plug and unplug constantly? Chrome/nickel plating might be a reasonable alternative.

Unless I use them every day, I turn external amps off when not in use because the 24 hour power drain being on stand by is a waste of power. Since most amplifiers need new capacitors every 15 years or so, and paying to replace them prohibitively expensive if even possible, I see no good reason to not turn the amps off. Leaving them on won't save the capacitors and when the equipment starts sounding like the speakers were draped in wet towels, replacing the amp is probably the most cost effective remedy.

I hope this helps.