So finally, after a significant number of tries/tests. I have been able to add most of the devices. The HEOS bar wants to be the master. By adding and removing the App a few times in a row, I was able to cheat and get also 2 x Heos 7s and one Heos 5 all added. What is clear is that the remote rear Heos 1s pair, and the sub-woofer, which are all linked to the Heos bar in a multi-speaker config, are not really available to your app. This in itself is not a problem as they are 'driven' by the Bar.
Is there any thought to add a sensitivity or management of Heos Rooms (i.e. groups of speakers)?
And unfortunately, the authentication module is still rather flakey and unreliable.
Some way to manually add devices and manage their IPs would be cool, too. All mine have fixed IPs...