The converter is the bridge between a MasterLink product/the ML master and the NL devices in your network.
That means, that the link products (e.g. your 3500) will follow your ML master as one unit.
Each NL product however, will appears as a device.
With the right settings (mapping of the sources etc) you will be able to hear/use the sources from the Essence on your Masterlinked products, yes (e.g. Netradio/TuneIn on the BV10.
And - if you have an Audiomaster with a cd-player - you could listen to the sound from it through your Essence.
I am not sure what you mean with ‘solution 7’ - maybe you could point me more directly to it (or post a screenshot) or even make a drawing of your actual setup and a describtion of your wishes.
There are plenty of users here, who can give you exact advice....if you have patience.
As for the ‘max of the ML units (junction box’), this has no influence on the converter, since it sees your ML-setup as one device.
The max of ML-linked product is determined from the ML-standart - I don’t remenber how many products there can be in the ML chain.....but it’s pretty many.
MM