Ideas to tidy up my system

[Opaloka1974]

Here is how my current setup is:
Yamaha arranger keyboard R+L outputs connected to Behringer XENYX Q502USB inputs 2/3 via 1/4" jack plug leads.
Focusrite scarlett solo audio interface R+L outputs connected to Behringer inputs 4/5 via 1/4" jack plug leads.
Novation SL61 MIDI keyboard connected to PC via USB cable.
Focusrite scarlett solo audio interface connected to pc via USB cable.
Behringer XENYX Q502USB mixer R+L outputs connected to powered speakers.
Ableton Live control surface set to Novation SL61.
Ableton Live sound output set to Focusrite Scarlett.
This allows me to play the Yamaha arranger and the SL61 together as the sound is mixed by the Behringer and outputted to the speakers. However to me its seems to be over complicated as I have 3 audio interfaces, one in the Yamaha, one in the Focusrite and one in the Behringer. I have tried removing the Focusrite and setting Ableton Live sound output to the Behringer and it works but there is no way to control the volume as the Behringer only has gain knobs for the jack inputs and not the USB (my current setup allows me to change the Ableton volume via the focusrite gain).
So my question is there any way that I could simply all of this. I don't need to record anything in the DAW and only use it host virtual instruments playable via the SL61 keyboard.
I have been looking at the Behringer UMC204HD audio interface which has a mix rotary knob that seems to allow you to balance the volume between the USB DAW and the input sources but not sure whether an audio interface can be used as a mixer for what I need.

[VariKusBrainZ]

What do you need the mixer for?
Do you have other gear?
Otherwise Id ditch that

[Nameerf]

I plug my synths through a line mixer into a Behringer UMC404HD and, like you say, use the monitor knob to hear either the DAW or the mixer.
The UMC404 outputs go to my monitor speakers.