Gents, I believe we may have found the core of the issue with the BV9 (or BV4 + BS4) setup. The BS5/BM5 has to be set to "AM = Yes" and "AM MODE = 0" under Roles (as previously described). However, the AV system has to be set to "Option 2". In other words, the BV9 has to be set to Option 2 (using the Beo4 or Beo5 remote control) not Option 1. This was prompted by Mr10Percent's prior comments / description of his BV7-40 setup.
Vladimir, it appears your dealer was right. You can use the BS5 in Audio mode without having the TV on. Just follow the above instructions or discuss this with them to enable the relevant setup.
Case closed (at least mine).