Another useful piece of information would be a human audiogram. The human auditory system is not linear, and that non-linearity varies with each listener. Nevertheless, in my personal experience, the best sounds come from systems that are linear in output with respect to input. That is, the output of the system is the same for all audible frequencies. Let the listener have a graphic equalizer if he wishes to emphasize the low notes, or attenuate the low frequencies because he lives in an apartment house. The same holds for the entire audible spectrum.

A quality audio system should be easy to use. Make it good and simple. Do not put 55 buttons on the system when 5 will do. Look at the design of other high end systems for both style and sound.

Determine the target market, the appropriate price for that market, and the competition for that market. There is a lot of competition for the high end, and every other end as well. What will be the cost to manufacture the system?

One question is the degree of digital vs. analog electronics that you need.

My orientation is that the most care and money should be spent on the speakers. The electronics are of secondary importance compared to the audio transducers.

Keep power consumption down, including when the system is shut off.

I hope that these ideas help.