It does not support playback from SD card, that slot is for firmware updates only (unlike the A8)
It DOES support DSD 5.6MHz, which the A8 currently does not. However, very few recordings are available like this; onkyo's website had about 10 for sale and nothing really interesting. SACD is all 2.8 anyway.
It comes with an app for Mac and windows called Fostex Audio Player; also works with the A8. It can playback all of these file types on the fly, up to 24bit 192kHZ PCM and up to 5.6MHz DSD. Communicates with the DAC over USB.
The best part: amazon has it for 36,000 JPY compared to the 80,000 JPY HP-A8. The A8 is AC powered and has more inputs and outputs (also a cool screen) but the bus power of the A4 is more than enough to drive fostex or denon headphones so I don't see the point. Also 32bit support is useless since nothing is available in that format anyway. A4 seems like a better buy and is also half the size. I will be using it with denon d7000s I got used in Japan a while back. I haven't seen any TH900 used yet and don't want to pay 130,000 for it.
Edited by Matvei - 11/14/13 at 6:30am