Originally Posted by 1200249
I put the AUX cable into the hole that says "LINE IN OPTICAL". Could you confirm again that the DAC isn't being used at all? Thank you very much.
I assume the AUX cable you're using is the same as for most mobile devices, which have a 3.5mm plug on both ends, but just to make sure, post a picture of it too. If that 3.5mm socket is purely an optical input (as there are compatible 3.5mm TRS-type sockets for these), then no signal will come out, and you'd need a 3.5mm to RCA cable to hook up your mobile device to the analog RCA inputs on the HDP.
If for example it still produces sound, provided one end of it is hooked up to an analog line out (like on a portable player, or a computer's earphone output), then that means the 3.5mm socket on the HDP is a combo jack, in the same way that some laptops used to output both analog audio straight to earphones or (with an adapter) digital audio through the same port on the laptop. It cannot possibly take an analog signal and just send it through and use its DAC section because it's an analog signal, unless it has an ADC. A Digital to Analogue Converter - whether the whole device, a part of it, or specifically just the DAC chip - takes the 10010101000010101110001111000101011 signal and turns it into an analogue electrical signal that your amplifier - whether an independent unit, or a section of one - will then amplify that signal to be able to drive headphones or speakers. The only way you can send an analog signal through a DAC is to use an analogue to digital converter chip first, and barring certain applications like recording, is a very round-about way of routing a signal and is therefore not likely done.
It is likely that the knob can select analog so the path from that combo jack will be selected depending on what signal is going into it.