@audiomaze if your question is directed at me, I was speaking of the tri vista dac. The v90 is a $300 dac that I would probably not attempt to work on. Parts cost would probably be more that the dac cost!
In general there are a few standard options to upgrading any component. Power supply capacitors, signal path capacitors, resistors in key areas and AC filter choke. After that convert to point-to-point wiring, etc.
Happy Listening
