What media were you playing into the HDMI input? I was running Amazon Music, so a stereo source. I didn't try it with a Dolby encoded source, maybe it is different. I'll check again when I get a chance.
It makes no difference as to what the source is or how it is formatted. All HDMI sources will be portrayed by the AV receiver while the AVR is set to its PURE DIRECT mode. The only thing that differs is the degree of processing available relative to that source. Dccoding wouldn't be negated though.
I've no idea as to why you aren't experiencing this. Maybe its an issue with the Fire Stick, but why would setting the AV receiver to PURE DIRECT cause the Fire Stick to start behaving differently?
EDIT
Just realised that you are talking about passing the source
through the AV receiver. Is this correct? If so then I'm not sure as to what that would result in and I'd have to run some tests. It shouldn't theoretically effect the ability to pass the unadulterated source straight through the receiver though?
What I did stumble across was with a digital source (Amazon Firestick into an HDMI input) that regardless of the audio over hdmi output setting, that audio disappears when switching to PD. I guess it makes some sense, who needs audio over the main hdmi out at any time with an AVR in place? Useful for another zone though.
Zone 2 HDMI out is technically independant of the main zone, but PURE DIRECT may limit or negate some of the processing associated with conveying digital audio to that additional zone?
You can actually get the AV receiver to mix multichannel sources down to just 2 channels while passing it through and still be able to depict that same source as a multichannel source in the main room. Not tried this in PURE DIRECT though.
It isn't possible to use the AV receiver's Bluetooth transmitter to convey audio if and when PURE DIRECT is engaged, but this isn't anything to do with a second zone.