You need your BS4 as an audiomaster, because your audiomaster must be able to distribute N.MUSIC and N.RADIO. BS Ouverture can`t do that.
You have four active speakers in your main room (room 1), I assume it`s wired 2x stereo...(?).
What about this: BS4 and BM1 in the mainroom with two active speakers (BL6000 OR BL4000). Connect BL passive to Masterlink, IR eye and CX100 in the linkroom (room 2) and set the linksystem to L.OPT 4. Install your Ouverure as a local source in the linkroom with one pair active speakers connected (BL4000 or BL6000). Set BS Ouverture to A.OPT 1. You can now control your Ouverture in room 2 by pressing RADIO, CD, A.TAPE...this will also activate your Beolabs. You have also access to all your mainroom soureces - RADIO, CS, A.MEM, N.MUSIC, N.RADIO...) by pressing LINK - RADIO, or LINK - CD, or L-N.MUSIC (it`s a one button for LINK-N.MUSIC). This will also activate your BL passive and CX100.
As an alternative you could try to connect PL output of your Ouverture to PL of the BL passive, but I`m afraid the Ouverture won`t activate the BL passive in this configuration. But if this will work you could use the CX100 for mainroom sources AND Ouverture as local source and keep your four Beolabs in the mainroom.
BTW - welcome to the Beoworld Forum.
Stefan