Why do you need a splitter? What are you trying to connect to what? The BD player already has your dual HDMI outputs which means you have a video connection for your TV and a proper audio connection for your receiver via HDMI. This SHOULD be a standard that all manufacturers have followed, but hey... f'k the consumer.
If you are looking to connect other sources to your receiver and the TV using a splitter to maintain that ultra hi-res 4K goodness, then you are outta luck.
The lowest common denominator issue will be at play and you will simply be unable to do what you are looking for. The receiver will demand video be in the format it supports (1080p or 4k/60) and the TV may ask for lower quality audio than the receiver supports. Whatever is the worst possible format will be the one selected.
A HDMI audio extractor can help you get audio out of a HDMI only device and pass HDMI video onto a TV while sending digital audio (via Toslink or S/PDIF) to your receiver. It won't be high def audio formats, but that's what happens if you want a video format higher than what your equipment supports. Sucks, but such is life. If you just need a HDMI 2.0 audio extractor, there are plenty of them, but audio quality will still be limited.
Your question was: " Now I'm trying to find a switcher that will allow me to send all the 4k to the tv, and send 7.1 audio via HDMI to the preamp for audio only."
Since your BD player already handles this just fine, it is VERY unclear what you are asking.
If you are asking about connecting your OTHER sources to the TV, then you probably should have mentioned that is what you wanted to do.
If you aren't interested in HDMI 2.1 but just HDMI 2.0, then I'm not sure what is up with your receiver not supporting it or what HDMI board it has, but you really are just going to have to live with limited audio from HDMI into your system because the gear you have simply isn't going to deliver. I would likely just use the optical audio output of the TV back into the receiver and call it done until budget allows for a HDMI board upgrade. I wouldn't consider a HDMI board upgrade if it wasn't to HDMI 2.1.