To the OP:
If you want to go into more power hungry planar magnetic headphones, then do buy a dedicated headphones amplifier. Please do. Take my word for it, it does make a world of difference. No matter how loud that receiver can get, even if loud enough to turn your headphones into mini speakers that does NOT mean it is driving them properly. You will need a good quality DAC and a nice amplifier. I would look at Audio GD, Schiit, JDS Labs O2, Burson, etc. All will do the job, but having good synergy will be a little bit harder to find though.
Ok now for the Beyer T1:
Before you even think about the T1, (I've owned them before) you will NEED a tube amplifier! Trust me, it makes sooooo much difference. I was using a Beyerdynamic A1 solid state amp ($899 amp) and it sounded meh....when my uncle let me hear my T1's on his Woo Audio WA22 it was a different world. You really have to invest in a good headphones amplifier before you go into Hi-fi right now you've in mid fi. A good quality DAC is important too, currently I'm using the DAC in my Burson HA160D, but while it is a highly regarded DAC I plan to upgrade it soon.