Re: Firmware 4.5.2 QC35 ii
> What is the firmware version that new headphones have in them?
It really depends on where you got it from and how long they were in stock before you purchased them. Could be any of the versions (especially if you buy off eBay). About a month or so back, I was in the Apple store and they had four QC35ii's on the shelf, one was the newer "AZ" version (that's the end of the serial number) which supports AR and three were the "AE" version (the original QC35ii type) and the AZ had been out a few months at that point.
> Is it possible not to upgrade the firmware?
Do not install and run the Bose Connect app. If you run it, clilck on the setting icon on the upper right hand corner. If it says "Your Product is up to date", then you have the current version which is 4.5.2. Otherwise it is probably downloading it to update your QC35ii and you should terminate the app as soon as possible. You can check what version you have in the app by click the settings in the upper right hand corner, sliding it up until you see "Product Info", select/tap it.
> Is it possible to upgrade the firmware to some other version than 4.5.2. and would you advise me to do that?
Not possible. Only thing you can do is let the connect app or the web download interface upgrade you to 4.5.2. There is no going back.