Yes, you can use an MCL 2A for the bedroom as link system for your BS7000 and connect the outputs to AUX input of your BS2500.
BUT, as the MCL output is a speaker level output, you will need a Hi-Lo converter (speaker level to line level)for this setup. Here in Euroland it`s a 10-15 Euro device.
Or you can go the "Masterlink-way". Connect an AUDIO AUX LINK cable to AUX socket of your BS7000 (main system), then connect a Beolink converter (1611) and install a Masterlink cable from BL converter to the bedroom. Now connect a Beolink active incl. IR eye and set the link system to L.OPT 4. The Powerlink output should be connected to AUX socket of your BS2500. Powerlink output delivers a volume controlled line level signal.
Third way is to connect both systems via AUDIO AUX LINK with a special crossover wiring. Now you can listen to both systems in both rooms.But it`s not possible to control the systems from linkrooms. You need to add a device like a BL active or an MCL 2A.
I don`t think an ML-MCL converter will help in your setup. It`s meant to add an MCL link system to "newer", masterlink equipped audiosystems like BS9000, 32000, 3000, 4...
Sorry, I don`t know, what a "X-tra room active kit" is. Are you talking about a BL active?
And I have no experience with an AV7000. I think, it was an US-only product...(?)
Stefan
Stefan