Hi guys, I'm looking to get a set of half decent headphones which I want to use for music from my HTPC, blu-ray movies from my PS3 or at a push the HTPC (which has a blu-ray drive, but to be honest I prefer the convenience of using the PS3, plus the prospect of HD audio when I get a new AV amp/speakers) and gaming on the PS3 and 360, perhaps a little PC gaming.
My current setup is super-budget stuff bar the HTPC, but I am in the process of upgrading everthing pretty much - will probably end up with a new budget Audio setup - Sony DG820 amp paired with Jamo A102 speakers. Samsung LE40A656 (arriving in a few hours!

) and I already have the PS3 and 360 and high spec HTPC/gaming rig (onboard sound though

).
Now - onto where I need advise... the headphones, and possibly a headphone amp/DAC to complement them. I have a pretty tight budget, but want to get headphones that are going to do a (relatively) great job of music and a decent job of movies and gaming too. I was looking at perhaps getting either the Audio Technica ATH-AD700s, Sennheiser HD595 or the HD600s as I think their slightly warmer and more laid back signature is the type of sound I would prefer, over something like the brighter Grado SR80s. Plus I'm sure my choices will be more comfortable to wear. I am also tempted by a cheap headphone amp or amp/DAC combo to squeeze a little extra performance out of the phones.
There are however, some things I really need help with as my understanding of this whole topic is limited to just a couple of nights research... e.g. very limited! Will my best bet be to just have everything running through the DG820 and then plug the headphones into this amp when I wish to use them, or would it be better to have the 'phones plugged into the HTPC for music (possibly via USB DAC/amp to bypass awful onboard sound)?
I realise the headphone socket from the Sony DG820 AV receiver probably wont be upto much, so I'm guessing running everything through the amp is not going to be the best scenario for decent sound quality when it comes to the headphones. Would simply using a dedicated headphone amp help improve quality of headphone jack from the receiver for all sources? Or would connecting headphones to a headphone amp via a non amplified line-out from the receiver be any better?
Will any budget headphone DAC/Amp give me improved sound quality for all the required sources in my setup (music from PC, movies/games from PS3) or is the best thing I can go for on a budget something like the Total Bithead simply to improve music through the new headphones by bypassing the HTPC's onboard soundcard?
Please can I have some help and opinions, as this whole headphones issue in my setup has really confused me!

Basically all I want is decent headphones, possibly helped along by a cheap headphone amp/DAC which will complement my new budget AV setup as described. More than anything, I want my music to sound great. If this means settling for the headphone out from my AV receiver for games and movies, and having a USB DAC/Headphone amp from the HTPC just for music then so be it. If I can get a headphone amp/DAC that will help with all three then that would be brilliant!
Thanks so much guys!