Andre,
I have an almost identical setup to you. (only my rear speakers are different).
Your description of your setup sounds as if you have it totally correct. (or correct as in the same as mine).
When you link the BL5's into a digital system (one with a digital output), you effectively lose all tonal controls and maintain volume. This is because the signal bypasses this part of the chip and exits directly to sp/dif. The Powerlink is required to singal on/off and to govern volume through the BV7.
You can change the tonal settings on the BV7 but this does nothing to the sound output of the BS5. Only to the sound output of the BV7 Video sources.
This is the intention of the BS5 and BL5 when connected digitally. Sound output is assumed to be manufacturers optimum setting. The same (I assume) would happen if you connected a non-B&O digital device to the BL5's. i.e. no tonal control with that either.
10%