Check this for information on filters (both PCM and DSD): https://kb.roonlabs.com/DSP_Engine:_Sample_Rate_Conversion.
As for the new ‘precise’ vs. ‘smooth’ filters – the release notes tell this:
New SRC filter choices: Smooth vs Precise filters. The Precise filters are steeper than the old ones, but designed around similar goals. The Smooth filters are ultra-slow-roll-off filters optimized for a very clean transient response. “Precise, Minimum Phase” is the new default.