the onboard realtek chip is one the worse sound that i have heard.. any pci sound sound performs better in term of sound quality or you can also consider USB DAC and it will be easier to state out your budget also.. so we can advise accordingly..

this kind of usb dac not usb adapter.. dont buy those cheap usb adapter.. it makes no different with realtek maybe even worse.. what you expect from a RM20 usb stick

i am using fiio for my sound processing but when i plug back the speaker to onboard sound.. i can feel immediate different between the audio quality..

you got the budget to replace motherboard but after you replace the motherboard your processor spoil how? u gonna spend again to repair or you are going to replace the whole set?.. why not spend it on a decent usb dac or sound card which u can carry from this desktop to another and maybe even use it on laptop... its a better investment still

dont spend on those fancy virtual multi channel sound processing... you can focus on decent 2 channel audio processor if you are not into gaming/you are not having multiple channel speakers set