Doesnt matter, looks like ive found my answer -
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Why is the headphone out so much more livelier then the line out?
edit: to answer myself more distortion it seems
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If your using to to drive another amplifer YES. Your overdriving the next device. It would raise the SNR and add distortion for sure as you said.
If your connecting a set of phonee to the line out, they would sound duller if your cans are high impedance as the line out is low power compared to the headphone output.
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I'm confused, what's the line out?
The RCA outputs. They are what's called line outputs. They are within the industry standard for line level. Amps have line inputs and line outputs...etc. You would use these inputs and output for connecting up to other consumer gear such as CD players, receivers, EQ's..etc. The can amplifier is just that a output with more amplification for your headphones.
Note, There is consumer line level which you would deal with when connecting consumer gear as was mentioned. There is also another standard which deals with line leve of professional recording gear. That is not really involved in this situation...
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If you intend to use the built-in amp then you use the headphone out.
If you intend to use a dedicated amp then you use the line out (RCA outputs).
If you've got a dedicated amp, you usually don't need to plug an amp into an amplified port.
Find out more about your headphones and whether they "need" amplification.
If they do what is the minimum (ohms) required to drive them?
So long as the ST's built-in amp can output at that level (they should cover most cans), you'll be fine.
If you've got a dedicated amp & it's specced to cover your headphones, again you're good to go.
