Lets say for example someone wants to make a DAC based on the AKM4499 or something, can they for instance ask for a schematic from AKM requesting what they need to do in order to reach the advertised specifications of the chip that they're selling to that person? And if they can request this, why not simply copy that design, and then simply add the finishing touches of staying within that design while also adding on personal features (like lets say this will also be a DAC you're selling that will support bluetooth).
Or the other example basically being, what exactly is used to verify AudioPrecision stuff for example? Also would it make sense for them to start offering solutions or "chips" or whatever, that are used when running the DAC portions of such measuring equipment. Or is this a case of "no this doesn't make sense for AP to use, because they can simply have their own products for sale, and since they are the cleanest, they can offer it at whatever price they want since no one else can come close to them aside from one or two other companies"?
In modern electronics there are various discrete components that a company can elect to use. One component is a DAC, a chip specialized in digital to analogue conversation, and this is usually provided by a third party such as Asahi Kasei. This third party will provide an evaluation board or similar during the prototype phase of building a new product. Their evaluation board will come with very detailed information, schematics and test suites to review, test and confirm each advertised feature.
There are plenty other dedicated components in a finished product. You referred to Bluetooth. This involves a combination of a Bluetooth chip (a radio chip) which may also cover other types of radio activity such as WiFi or wired networking. The more it does, the more complex the chip, and the more complex the software running that chip tends to be. A lot of product categories in the technology industry use Linux-based networking stacks to address this.
This networking capability will have its own evaluation board for the prototyping stage.
And now we move to other chips. General I/O (input/output) around digital connectors such as USB. I notice XCOM is popular in the audio world. Another evaluation board. This evaluation board may also have some more generic I/O to address things like optical (another chip) and so on.
Now you have a bunch of evaluation boards provided by various companies. Each board has a defined set of activities. You string them together, with the interconnecting glue either provided by hardware or - in more sophisticated setups - via software. You test out the combination to make sure everything works. You probably have to make adjustments. Let’s say the XCOM is making a call to a register that the networking chip is also calling. Change the register for one, no more congestion. And so on.
When you have everything working, and your input/output materials meet your requirements, you now know how to build your device. You send a prototype order to a manufacturer and they send back a completed combined circuit board. You test, fix and revert.
When all this is done, you have a product working according to spec. You can then move towards production.