Years ago I had a setup with BV7-40 as videomaster and BS7000 as audiomaster, connected via BL converter to the Beovision and with an MCL linksystem connected to BS7000. This included several MCL2A links, an MCL2AV for active BL5000 speakers in a linkroom and a BL video for the MX4000 in the bedroom. It was possible to access all sources - audio and video - from every room. I know, Beo doesn`t recommand solutions like this, with a ML system and an MCL system in parallel, but it is working great. Should also be possible with an LX5500 (it got the AUDIO AUX LINK connection too, I think ??) or with an MCL2AV.
Hope this helps
Stefan