Honestly, that would not be a good option as you would be throwing good money at a bad option if it worked at all. This board's primary design is all about PCIE 4.0. When you match levels of engineering together you get mathematically predictable results. If you are set on using that CPU the best option would be to use a board that is technically matched to it by design. You will not get any gain by using that cpu on this board and in fact it may not go well at all. Your best results would be to use a board that was designed for a 1st gen cpu. The thing is, the only way you will get the number

Typically MotherBoards come with BIOS that is reasonably up to date, I can't speak to this one. You can't boot to POST without a processor and RAM (and power supply). You need to boot at least to the POST to update the BIOS. So if your processor won't boot on the old BIOS then you can't update it. If it will boot on the old BIOS then you can (by USB I am sure would work).

1st thing im assuming you meant 2133 mhz and not 21333, as otherwise i would have no clue what the issue could be. If my assumption is correct the following should work, In bios if you go into advanced mode (f7 by default) and into the Ai Tweaker tweaker, there will be a dropdown for Performance Enhancement. In the dropdown select the setting called D.O.C.P. It should update the Memory Frequency dropdown to D.O.C.P 3600, if not you should be able to select that from the dropdown.