Please don't mix HDMI EDID exchange and HDMI CEC exchange. EDID is a capabilities exchange running on I believe pin 21 but need to check to be sure.
EDID runs on a peer-to-peer basis between both ends on the cable. Mostly it is forwarded by the AMP to the TV transparently, but if the AMP is set to do any Video processing then it is intercepted and handled locally. Audio is always intercepted by the AMP but may be forwarded depending on settings next. Sync issues and Audio / Video capabilities are typical EDID related.
HDMI is a bus protocol and works on all units interconnected via specific addressing or broadcasting. ARC not working , Remote control pass-through Single touch operations, sync power on/off, audio auto switching etc not working are all HDMI-CEC related.
HDMI-CEC only does something when a unit is switched on/off or when the IR remote control is operated (=always triggered by a human action). EDID does something when the audio/video stream is changed in any aspect. By cutting pin-13 or using a blocker HDMI-CEC is disabled for sure, but EDID is not and should not be as it is essential.
1) Q10 and Q5 don't support HDMI-CEC at all and worse may cause other devices not to interwork correctly anymore. Mostly this happens during the powered-on state, but I am not so sure android 7 behaves correctly during powered-off state (no problem with 5)? Looking for a blocker already myself.
2) Loosing ATMOS support when using a blocker (pin-13 removed) is implausible by me as various audio modes support is never handled/influenced by HDMI-CEC in any way. The root cause must be somewhere else.
3) Using HDMI-splitters may have unpredictable results as the HDMI standards never were designed to include this functionality. Communication wise splitting and correct HDMI EDID operation (=peer-to-peer handshake) are highly conflictive, no matter how smart it is. Using a switch is not a problem as cascading is foreseen in the standards. The HDMI panel within an AMP acts as a switch too. HDMI signals are never meant to go to multiple destinations in parallel from a single source. A device needs to have multiple outputs for that with independent video/audio processing for each port which only real professional/expensive splitters typically offer. Want to see one? Just go to a big TV shop and ask what they use to get their demo's to multiple TV's at the same time.