I posted my question below earlier on the DX50 thread, but just noticed this thread & will post my Q here since my aim is to use the N7's USB audio port along with the DX50 as the DAC/Amp:
Anyone tried using the latest Nexus 7 USB Rom with the DX50?
Supported USB audio devices
These are just some of the supported USB DAC's: CM106-F, FiiO E07 + E10 + E17, Hifimediy Sabre, VIA USB Audio Dongle, Behringer UFO202 + UCA202 + UCA222, Syba SD-CM-UAUD, Miditech Audioface2 (PCM 2902), FujitsuSiemens PortReplicator (CM 108), Aune T1 (TE7022), Turtle Beach Micro II, BERESFORD Caiman, Teralink x2, Headroom Total Bithead, Fostex PC-100USB.
Basically all standard USB audio devices should work.
Problems have been reported only with TAS1020B based DAC's.
The DX50 is not listed, but I'm trying to find a way to use it as a DAC since Ibasso is still awaiting for certification of its drivers from MSFT.
Apparently, the iBasso DX50 can't work with a Mac: it is not a standard USB DAC.
As far as I know, existing Android USB audio implementations are only compatible with standard USB DAC, i.e. compatible with USB Audio Class (1 or 2) standard.
Anyway, you could try to connect your DX50 with a Nexus 7 using:
. USB Audio Player PRO (UAPP):
UAPP includes its own USB audio soft driver.
There is a free trial version available on Google Play store
. the native USB audio of Android L: