Surround issue

I connected my sound bar and my 2 radiant speaker to the hub and I got a surround system, if find it amazing. Unfortunately my sound bar is much more powerful than the radiant speakers and this application doesnt let me change much (only from -6 to +6) the volume individually, so the sound of the radiant speakers are too low.

Lipe montreal about Wireless Audio - Multiroom, v3203