Is it likely that a firmware update will give 3rd party apps access to DP-X1 DACs?
Honestly, I don't see any proof that they AREN'T able to access it. 3rd party audio apps sound literally the same to me as the stock app with the same files. It'd be silly for Onkyo to implement the Android OS otherwise. I've only seen issues with apps that are purposefully written to use CPU decoding. Apps that use the standard Android APIs for audio handling sound literally exactly the same as the stock player app. There's literally no reason why they wouldn't, from a technical perspective. Onkyo writes the drivers that interact between the Android audio subsystem and the hardware. All digital audio needs to go through this subsystem at some point to be transformed into analog audio. That is being done by the DAC chip. The 3rd party apps that are using the CPU are doing extra processing -- they're decoding the audio files with the CPU to transform them into a known digital waveform, which then gets sent off to the internal DAC (and gets sent to the amp and then to the physical headphone outputs). There is literally no way for the audio to go to your headphones if it doesn't go through the DAC chip.
Now, the 3rd party apps may not be making use of the hardware decoding. The DAC chips have built-in hardware support for many formats -- FLAC, MP3, APE, etc (as well as standard PCM wav). When apps are written to make use of the hardware (that is, they offload processing to Android), they can send those native formats as digital samples directly to the DAC chip, which does hardware decoding of those formats (and converts the digital signals into analog signals, which get amplified by the internal amplifiers, and sent out of the headphone jack). Onkyo would have written the Android audio driver as such to let Android know which formats were natively supported by the DAC hardware. These formats would get sent natively, without any CPU processing, to the DAC chip for decoding. This should be completely seamless as far as software goes. For an app developer, they would simply call the Android audio APIs and pass in the file. The Android audio subsystem handles the rest. If the DAC hardware doesn't support a format, the Android audio system then falls back to using the CPU -- either the CPU may support the format natively in its own DAC, or there is a software implementation for decoding the format which make use of the general purpose CPU to do the math necessary to produce a waveform. The 3rd party apps that have been reported as having trouble are explicitly written to do this last, least efficient process. For every file format, they have a software library that uses the general purpose CPU to convert those formats from, say, MP3 to PCM WAV using the CPU exclusively. This waveform is then passed to the DAC, where it is converted from a digital signal to an analog signal, and is then sent through the amplifiers and out the headphone jack. See, even when the 3rd party apps bypass the built-in CODECs in both the DAC chip and CPU, they still need to use the DAC chip to convert a digital signal into an analog one. There's no way around that, so they are definitely using the built-in DAC chip. If they weren't, you'd have no sound output, and that's clearly not the case.
To my ears, 3rd party apps are definitely making use of the internal hardware. Playing the exact same files, the sound output is exactly the same as with the stock app. So, even if 3rd party apps WEREN'T using the internal hardware (which they totally are, but for the sake of argument I'll let it go), they sound exactly the same as the stock app, so what does it really matter? No matter what, the audio sounds great, and that's the entire point. If you can't tell a difference, does it really matter? Just enjoy the device.
