no point buying a amp for the p5's, the were designed more for the ipod and therefore wont require extra power. they not a bad start but for long listening sessions i find the leather ear cups to cause abit more sweat than i like on my ears. my advice would be to rather go for something more circum-aural (fits over the ear, not on them like the p5's do) this will lead to greater comfort and sometimes better imaging (something that is nb for gaming). the sennheiser 5 range are supremely comfortable, but they may be a bit on the light side of bass.
also they are open back which means they leak sound and also let outside noise in, but i find open backed headphones are better suited for long listening applications (like gaming and long pc sessions at work). as for a amp, most dedicated headphone amps wont accept toslink(optical) as headphones are stereo and digital is used mostly for surround sound. there are many options for a dac out there ranging from expensive to rather cheap, but for games and basic mp3's i would be surprised if you saw a massive difference by adding a dac.
headphones all generally have their own audio signature, senn's are clear but low in the bass department, grado's are more aggresive sounding than senn's which can be very laid back. then on the opposite side of the spectrum you get cans like the monster beats which are more bass heavy (and surprisingly very good for gaming i find). for games i personally prefer my reference pioneer se a1000 cans, they REALLY comfortable and the sound is highly detailed and balanced (no excessive boom) which is great for games and for R1000 they are awesome value. i have em hooked up to a cheap-ish pro-ject headbox 2 which i feel does the job quite nicely, but one day i will upgrade to something meaner. for music my senn hd 598's come out to shine (or i just leave the pioneers in) and when im in the mood for some good ol rock then its the beats turn to shine.
