I don't have an Oppo but all players are pretty much the same with respect to how they handle various output options.
i am going into a 2 channel preamp. so oppo told me to set digital out to PCM, set HDMI to off, and set the LPCM rate to 192 khz. this works and it sounds great. the only catch is it sends ALL audio out the coax.
Setting the digital out to PCM indicates you want to use the digital outs and output PCM. It probably also has a setting for 'bitstream' which basically just outputs the bits without any processing so you can send them to something else like a receiver/pre-pro with a decoder for the format (like DD/DTS). Note that if you set it to bitstream but play PCM (such as a CD), it will still work because PCM doesn't need to be decoded, just separated into channels.
Setting the LPCM setting specifies the sample rate you want to use and does not apply to bitstream output. Typically you just set it to the highest sample rate your receiver/pre-pro can handle. If you were to set LPCM to say 96 kHz but play a 192 kHz track, the player will downsample to 96 kHz; that's why Oppo says to set it to 192 kHz - it can handle 192 kHz and that's what you want output without touching it.
anyways i noticed that the i also have the option of not turning HDMI to off but to LPCM (which still allows me to chose 192 KHz under the LPCM rate). would this allow me to pass 192 by coax and still pass audio by HDMI to my tv for watching movies?
No, it will decode a multi-channel format and turn it into multi-channel PCM. You would set that if your receiver/pre-pro does not have a decoder for the multi-channel format but can handle multi-channel PCM; in other words this is setting the player to do the decoding instead of the receiver/pre-pro.
It is similar to setting the digital out to PCM but playing a multi-channel format like DD/DTS. The player will do the decoding, downmix it to 2 channel PCM, and then send it out the digital out.
Again the LPCM setting just sets the sample rate.
Note: many people are still confused by PCM vs LPCM setting. The acronyms are for the same thing: Linear Pulse Code Modulation so calling the setting for sample rate LPCM is confusing, but on every player I have ever seen all it does is specify the sample rate and is how you control whether the player should upsample/downsample or leave it alone.
I'd bet if you set the digital out to PCM and keep HDMI ON (if possible), it will send the digital audio out the coax but send the video out the HDMI out.