I have posted some brief impressions of the AT-HA5000ANV combined with the ATH-W3000ANVs in the amplifier section of the Forum for anyone who may be considering that amp. for their ATH-W3000ANV or other Audio Technica headphones.
I have owned my AT-HA5000ANV now for just over 3 months. I have been hesitant to comment on it earlier, as I also had purchased the ATH-W3000ANV headphones at the same time, and it has taken me a few months to develop strong impressions of both, compared to my other current setups and previous setups I have owned.
My current setup is MacBook Pro>iTunes/Amarra Mini> USB RWA Isabellina (original version)>AT-HA5000ANV. I can use the Isabellina as a stand alone DAC...
I agree with n3rdling. or otherwise you may end up buying and selling a lot of equipment before you find what you like. From your description of the music you like though, IMO, you are going to eventually want to have more than one headphone.
One place you can buy Oyaide online in North America is at Planet of Sound's (Canadian) distribution centre website. I have no relationship with them, but recently bought some Oyaide RCA cables from them.