We are all noobs at one point.
The short answer is "yes" to all your questions above.
The longer explanation, more power does allow for more volume, but even if you "turn it down" to match the volumes at the same comfortable listening level, a more powerful amp will have more body in the bass and high treble frequencies, and many other small improvements that result from the muscle to drive headphones at their full potential. Different headphones will scale up differently. I haven't heard the Sennheiser HD598 myself, but from what I've read, either FiiO product would sound very good & provide an improvement from plugging directly into your smartphone, though the HD598 is sensitive enough that there may not be a very big sound quality difference between the E17 and E12 – somebody who owns an HD598 would be able to give you a more accurate impression. As a general rule of thumb, the less sensitive and the higher impedance a pair of headphone is, the more it benefits from more power.
That was mostly focusing on your headphones and amping, but what about the other end: your source, the Galaxy S smartphone? As far as I know, you can't use the E17's DAC to replace the DAC built into your Galaxy S, the DAC "half" of the E17 is meant to be used with a computer or sound system. You CAN use just the amp portion of the E17 with your phone, by connecting your phone's headphone out to the E17's analogue input, but then you would be using the E17 like a less powerful E12. I'm not saying anything, I'm just saying
Some people do use the E17 just as an amp when they're out and about, then make use of the DAC + amping features when they are using a computer at home or the office.
In the end, they both have their strengths (else why would FiiO make both?), and it's up to you to choose what will benefit you most
Good luck, have fun!
Originally Posted by Dyaems
woah, im seeing capacitors in the pic.. might change them when after the warranty runs out haha
Of course there are capacitors inside the amp
By the way, FiiO announced that they're releasing a special DIY version of the E12 for people that want to tweak with the components Edited by Evshrug - 1/1/13 at 3:46pm