If you have a Beocenter 2300 capable of two-way infrared communication (type 27xx, produced 1992-93), you should be all set — regardless of the capabilities of the MX 4000 and the DVD 1. Connect the audio and video systems with an Audio AUX Link cable (7-pin male-to-male DIN) and put the audo system in option 2 and the video system in option 0. With this setup, all IR commands and feedback are routed through the BC 2300.
There are also chances that you have a two-way capable MX 4000. Mine is a type 3527 from 1992 and it can be controlled directly with a Beolink 7000 (although I prefer the Beolink 5000 for daily use). If your's happen to be a similar, early-generation MX 4000, you can set both audio and video system to option 1. In this case, there's no need for the Audio AUX Link cable, unless you want an integrated A/V system.
The DVD 1 is controlled by the television. Connect it to the AV2 SCART and configure as "CDV" in the MX 4000 setup menu. You may also have to reconfigure your Beolink 7000 remote in order to activate the CDV (DVD) selection.