LPCM will be the one to use here.
Unless you are playing some content using SDIF2 or DSD (never come across Blu-Rays or TVs using these myself), bitstream on the Oppo will likely be referring to formats such as Dolby Digital. The Rossini will not work with these, so for compatibility and quality stick with LPCM.
With the sample rates, this is completely content dependent, Watching the news on your TV will likely be a different sample rate to a Blu-Ray, so there won’t be one perfect setting for all if you want to avoid the Oppo doing any upsampling or conversion.