On my BS3000 I use the wall bracket that I bought for my BeoCenter 2300.  I wonder if your bracket is different from mine, which evidently remained the same across generations.

The bracket system comes with two metal handles that you screw into the BC2300/BS3000.  Meanwhile, there is a black plate which you attach to the wall.

Once this is done, there are hooks (on the plate I believe) which catch nicely on the handles.  Small slots into which the hooks slide prevent any slippage.  The sistem is held by pure gravity.

I still recall 26 years ago hanging my BC2300 from the wall and not being sure if I could let go.  It seemed the B&O could tip forward and crash to the ground!  But it is a secure system.

Let us know how it goes.

In two different homes of mine I ran the wires through the back of the wall, as you appear to have done.

That Lewis design is now over three decades long, but when mounted this way, I always felt, to this day, that I was looking at some Utopian future where devices are magical.