Bluealsa (mixed stream) send output to headphones

[audiocore]

i there,

I'll try to explain what I want to achieve My setup consists of a Rapsberry Pi 3b with a Hifiberry DAC+ DSP.
The DAC+ DSP mixes a digital input (TV) with the internal sound stream of the Raspberry. This stream can be controlled by alsamixer or dsptoolkit from hifiberry.

aplay -l gives:

Code:

**** List of PLAYBACK Hardware Devices ****
card 0: sndrpihifiberry [snd_rpi_hifiberrydacplusdsp_sou], device 0: Hifiberry DAC+DSP SoundCard HiFi dacplusdsp-codec-0 [Hifiberry DAC+DSP SoundCard HiFi dacplusdsp-codec-0]
 Subdevices: 1/1
 Subdevice #0: subdevice #0

and amixer -D gives:

Code:

Simple mixer control 'DSPVolume',0
 Capabilities: volume
 Playback channels: Front Left - Front Right
 Capture channels: Front Left - Front Right
 Limits: 0 - 255
 Front Left: 198 [78%]
 Front Right: 198 [78%]

Until now, only the "moode audio sound" is transmitted by bluetooth to my headphones. What I'd like to do is, to transmit the mixed sound (TV sound ) to my bluetooth headphones.
 
Bluealsa (v2.1.0-40-g313b00c) is working and sudo bluealsa-aplay -L gives me:

Code:

bluealsa:SRV=org.bluealsa,DEV=xx:xx:xx:xx:xx,PROFILE=a2dp
   WH-1000XM2, trusted audio-card, playback
   A2DP (SBC): S16_LE 2 channels 48000 Hz

 I can configure my device with amixer and also play sounds

sudo amixer -D bluealsa sset 'WH-1000XM2 - A2DP' 100% or play sound...
aplay -D bluealsa:SRV=org.bluealsa,DEV=xx:xx:xx:xx:xx:xx,PROFILE=a2dp sample.wav

How can I now send the complete stream or what comes out from DSPvolume via bluetooth?