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Crosshair VII Hero Oscillators

Level 7
Are there any experts here who know how the PLL and reference clocks work on this motherboard?
Unlike most people here who are using the motherboard for gaming, I am planning to use it for high-end audio reproduction. We do a lot of crazy things in the hi-end audio world. One of these crazy things is replacing the the stock oscillators with very expensive OCXO clocks that most of the time cost a lot more than the motherboard. And I am looking to understand a little better how those oscillators are used, so it can give me an idea which oscillators would be useful to replace and which not.

Here is a picture where I highlighted some of the oscillators on the motherboard.

#1 - used by the chipset
#2 - ?
#3 - ?
#4 - ?
#5 - LAN
#6 - audio?
#7 - audio

First question I have is - does anyone know what #2, #3, and #4 are used for?

The second question is - I was able to replace the chipset clock (#1) successfully. And I can power the clock on or off easily in real-time by a flip of a switch. I expected that motherboard would not post or boot with this clock off. But it does. It posts and it boots. And if I play music through a USB port connected directly to the CPU, it plays fine. If I play music though a USB port going through the chipset I don't get any sound when the clock is off. As soon as I turn the clock on, the music starts playing. So my question is does anyone know how the computer boots without this clock? Is there a free running clock in the X470 chipset?
Someone else using the X370 chipset (Crosshair VI Hero) reported that his motherboard does not post without this clock. I have been scratching my head trying to understand this.

I have a couple other questions if there are some experts who can help, but let's do one thing at a time. Your help is highly appreciated. Thank you.