Your are correct, and HP has not done a great job on this. I think it is just too detailed and numerous to get them all right by the team trying to keep all the drivers straight. I posted here some multiple weeks back on the opposite..... the listings in the advisory were not updated but you could find the right BIOS updater by going to the workstaton's drivers site. Now this.
So, you will not find that updated 2.77 BIOS through the HP drivers page for your workstation, but you are so close.... Why did you not click on the link in the advisory you posted? The link there is correct and works. I've posted here many times on the safest way to update BIOS.... to do it from within BIOS. Attached is a pic of the navigation to the .bin file you need to have on a thumb drive to update from within BIOS. As you can see it is 2.77. Here you go....... straight from SoftPaq from the advisory you linked to:
