If you use that method to connect to your amp, you will be using the digital to analogue chip in your laptop/mobile. Therefore the limiting factor is the quality of components in those devices.
It looks like you have already been given similar advice in another thread.
- if your amp has digital inputs then
a) check your laptop model to see if it has an optical digital output (often these are ‘hidden’ in a combined optical and RCA output. If your laptop has one, you can connect directly to your amp’s digital inputs
b) if not, you would need a converter device to get the equivalent effect. You would be looking for a ‘USB to coaxial/optical audio converter’ in order to connect your laptop to your amp’s digital inputs
- if your amp doesn’t have digital inputs then you need a DAC. This would connect to your laptop’s USB port and convert the audio to analogue to allow you to connect to your amp’s line/RCA inputs.