This settings are meant for HD audio playback at 24bit depth and 96000Hz frequency. So there's no need to change anything default if your audio sources have standard CD quality.
defaults.pcm.!rate_converter "samplerate_best" defaults.pcm.dmix.!rate 96000 defaults.pcm.dmix.!format S24_LE
An exclamation sign causes a previous definition to be overridden. This syntax can be used with any configuration file assignment.
Dmix is enabled as default for soundcards which do not support hardware mixing.
Since Pulseaudio server is not intended to deliver high quality streams for the sake of usability, it is recommended to just not install it.
resample-method = src-sinc-medium-quality default-sample-format = s24le default-sample-rate = 96000
SRC resampling algorithm is very cpu intensive. Setting it to medium quality should work better.