How to disable pulseaudio permanently in Ubuntu 16.0.4 LTS

Question

I am running our gaming application of embedded hardware running ubuntu 16.0.4 LTS.

I want to remove pulseaudio modules and use ALSA directly from our application.

I removed pulseaudio using the following command:

sudo apt-get --purge remove pulseaudio

After that I rebooted my system to let the ALSA take over as default sound system without pulseaudio.

The sound cards listed in /proc/asound/cards are:

0 [HDMI           ]: HDA-Intel - HDA Intel HDMI
                  HDA Intel HDMI at 0xf7430000 irq 33
1 [NVidia         ]: HDA-Intel - HDA NVidia
                  HDA NVidia at 0xf3080000 irq 17
2 [amplifier      ]: USB-Audio - 4.1 amplifier
                  4.1 amplifier at usb-0000:00:14.0-5, full speed

Output of aplay -l is :

**** List of PLAYBACK Hardware Devices ****
card 0: HDMI [HDA Intel HDMI], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: HDMI [HDA Intel HDMI], device 7: HDMI 1 [HDMI 1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: HDMI [HDA Intel HDMI], device 8: HDMI 2 [HDMI 2]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 7: HDMI 1 [HDMI 1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: amplifier [4.1 amplifier], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Output of aplay -L is:

null
    Discard all samples (playback) or generate zero samples (capture)
pulse
    PulseAudio Sound Server
hdmi:CARD=HDMI,DEV=0
    HDA Intel HDMI, HDMI 0
    HDMI Audio Output
hdmi:CARD=HDMI,DEV=1
    HDA Intel HDMI, HDMI 1
    HDMI Audio Output
hdmi:CARD=HDMI,DEV=2
    HDA Intel HDMI, HDMI 2
    HDMI Audio Output
dmix:CARD=HDMI,DEV=3
    HDA Intel HDMI, HDMI 0
    Direct sample mixing device
dmix:CARD=HDMI,DEV=7
    HDA Intel HDMI, HDMI 1
    Direct sample mixing device
dmix:CARD=HDMI,DEV=8
    HDA Intel HDMI, HDMI 2
    Direct sample mixing device
dsnoop:CARD=HDMI,DEV=3
    HDA Intel HDMI, HDMI 0
    Direct sample snooping device
dsnoop:CARD=HDMI,DEV=7
    HDA Intel HDMI, HDMI 1
    Direct sample snooping device
dsnoop:CARD=HDMI,DEV=8
    HDA Intel HDMI, HDMI 2
    Direct sample snooping device
hw:CARD=HDMI,DEV=3
    HDA Intel HDMI, HDMI 0
    Direct hardware device without any conversions
hw:CARD=HDMI,DEV=7
    HDA Intel HDMI, HDMI 1
    Direct hardware device without any conversions
hw:CARD=HDMI,DEV=8
    HDA Intel HDMI, HDMI 2
    Direct hardware device without any conversions
plughw:CARD=HDMI,DEV=3
    HDA Intel HDMI, HDMI 0
    Hardware device with all software conversions
plughw:CARD=HDMI,DEV=7
    HDA Intel HDMI, HDMI 1
    Hardware device with all software conversions
plughw:CARD=HDMI,DEV=8
    HDA Intel HDMI, HDMI 2
    Hardware device with all software conversions
hdmi:CARD=NVidia,DEV=0
    HDA NVidia, HDMI 0
    HDMI Audio Output
hdmi:CARD=NVidia,DEV=1
    HDA NVidia, HDMI 1
    HDMI Audio Output
dmix:CARD=NVidia,DEV=3
    HDA NVidia, HDMI 0
    Direct sample mixing device
dmix:CARD=NVidia,DEV=7
    HDA NVidia, HDMI 1
    Direct sample mixing device
dsnoop:CARD=NVidia,DEV=3
    HDA NVidia, HDMI 0
    Direct sample snooping device
dsnoop:CARD=NVidia,DEV=7
    HDA NVidia, HDMI 1
    Direct sample snooping device
hw:CARD=NVidia,DEV=3
    HDA NVidia, HDMI 0
    Direct hardware device without any conversions
hw:CARD=NVidia,DEV=7
    HDA NVidia, HDMI 1
    Direct hardware device without any conversions
plughw:CARD=NVidia,DEV=3
    HDA NVidia, HDMI 0
    Hardware device with all software conversions
plughw:CARD=NVidia,DEV=7
    HDA NVidia, HDMI 1
    Hardware device with all software conversions
default:CARD=amplifier
    4.1 amplifier, USB Audio
    Default Audio Device
sysdefault:CARD=amplifier
    4.1 amplifier, USB Audio
    Default Audio Device
front:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    Front speakers
surround21:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    4.0 Surround output to Front and Rear speakers
surround41:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    IEC958 (S/PDIF) Digital Audio Output
dmix:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    Direct sample mixing device
dsnoop:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    Direct sample snooping device
hw:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    Direct hardware device without any conversions
plughw:CARD=amplifier,DEV=0
    4.1 amplifier, USB Audio
    Hardware device with all software conversions

When pulseaudio was installed and running in the system, I selected 4.1 Amplifier device in sound settings for Output and I could hear sounds in sound test. Even VLC Player also worked fine.

But now after uninstalling pulseaudio,I am trying to play sounds on card 2 USB-Audio - 4.1 amplifier devices listed in aplay -L but the volume is so low that I can bearly hear any sounds.

I made sure that the volume is unmuted and set to 100% for 4.1 Amplifier sound card in alsamixer but still the volume is super low.

Not sure what is happening here ?