Wow - Tspeer - Blast from the Past and the dongle/jig club (brotherhood of the travelling dongle?)! I'm pretty sure I MIGHT still have one dongle around somewhere along with the update CD and the DTS-MA bomb patch CD. I had 10 of those things I made using FFC and they all disappeared over time. Sadly my 805 is no longer in service (though I still have it). The center channel went out on me. I upgraded to a Denon X4000 which I had for over 6 years and only just recently upgraded to a Denon X3600 so I could pass HDR thru as well as hirez audio.I used to have a link in my sig to an ISO I made with the 805/875 firmware and software to update it. Looks like the forum has had a makeover and the sigs are all gone. If anyone needs that ISO, I still have it and can host it: http://www.goodboy.mygamesite.net/xx5_Onkyo_UpdatesISO.zip LOL, my own malwarebytes browser guard blocks it, likely because I have never bothered to install a cert and enable https. It's safe.
I barely remember how to do it. If your main updater version was v1.01 or later, no jig was needed just the resistor thing. Schematics for that are included. A document with all of the directions is included. You will also need a usb to serial adapter, these are cheap and easy to find on Amazon for less than $10.
If there is anything newer earlier in the thread, disregard. Just came across an old saved shortcut so thought I would pop-in. I made a jig (maybe 2?) with some donations from forum members, and shipped it off to someone ages ago. The idea was to just keep passing it on to others as needed. Whatever happened to it? lol I think I sent out a few of the little resistor things as well for people on main updater 1.01 or later in which case the jig wasn't needed.
As for my 875, still using it. I have a 4k tv, just have that directly connected to the Xbox X, and use optical out to the Onkyo. When I got this receiver, I also got a cooling fan mount that sits on top and comes on when the 875 is powered on. Hopefully it has helped extend the life.
As I recall, if you had MainUpdate 1.00 you needed a jig or dongle. 1.01 you didn't
PS - I've still got the ISO shared on my Google Drive as well if anyone needs an alternate location to download from.