I have been using the JBL MA510 for several months now, paired with JBL's 250B bookshelf speakers, 220P powered subwoofer, 245C center channel speaker and 240B surround speakers. Overall I could not be happier with the performance and quality of the system components. After going through the process of balancing power levels from each speaker and performing room equalization, the sound is amazing and produces a great home theater experience. Playing music through the Bluetooth input is an equally rewarding experience.
I have only one complaint with the MA510, which is that the startup behavior is fundamentally uncontrollable with respect to the selected input source. The MA510 insists on automatically selecting the first active input it finds. For me this means that before I can use the system, I have to wait for the MA510 to initialize and then manually select the desired input. I have to go through this little drill every time I turn the system on.
I have the following equipment connected to the MA510:
HDMI Out (eARC) - Sony Bravia XBR-65X810C
HDMI 1 In - Fire TV Stick 4K (YouTube TV, Netflix, etc.)
HDMI 2 In - Sony Blu-ray Disc Player BDP-S500 (a true antique!)
The Sony Bravia is relatively old. Streaming apps don't perform well on it when using the ARC interface, producing streaming hiccups and down-converted audio modes. None of this is a problem with a newer streaming device like the Fire TV Stick 4k, and CEC controls work well. Once the Fire Stick is the selected input source, I'm then able to do everything with the Fire Stick remote. However, the system always selects the TV (ARC) input on power up, so I have to go through the input selection drill with the JBL remote before I can use the system.
This could be easily remedied if JBL/Harman would add a general configuration option to control the default input selection. The default selection could be "Auto" which would leave the current system behavior unchanged. Another selection could be "Last" which would continue using the selected input source when the system was last used. Those two options would solve my problem, and instead of (or in addition to) "Last" it would also be possible to make the other input sources available as selections. This would allow me to control the system using only the Fire Stick remote, unless I need to change the input source or make some other change through the MA510 menus.
The smart auto-select function is great unless it doesn't do what you want, in which case it feels more like a broken feature. There needs to be a way to stabilize this behavior, so that it works more like the input selection knob on an old Hi-Fi audio receiver. It's a shame to have this minor firmware oversight in what is otherwise an amazing high performance audio system.