External HD Changing the quality of the sound?

Oh, if you are using a USB connection on your DAC, use a FW or Thunderbolt drive. If you are using a FW-SPDIF connection, use a USB DAC.

i have the G-Drive 2tb with firewire800 :)
I use itunes to manage my library (yes i know the bads about it, but i have too many music and the way it's displayed for me is easy to manage how to play my music)
So how can i set it to the memory cache? O_o

and it's better to use a different type of connection for my audio source than a dac or so it will take the power from it, isn't it right?

I too use iTunes. But the Mac version is better integrated with the OS from what I understand than the PC version and it is a great way to organize album meta data and playlist. I just organize them once and it works for my music servers and iOS/iPod devices as well.

To use memory play, try BitPerfect from the AppStore. It's a very simple, very easy to use plug in to iTunes. It bypasses iTunes' playback engine and sounds very good.

It's IMHO a close second to Audirvana Plus (which is still affordable) and A+ provides the option to play DSD files as well, if supported by the DAC (it will convert DSD to PCM otherwise). If you only have primarily RBCD or HR PCM, BitPerfect will work just as well.

PureMusic and Amarra IMHO are much pricier and not worth the added moolah.

so BitPerfect auto-select the memory cash?