aconnectgui software package provides graphical ALSA sequencer connection manager, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install aconnectgui
aconnectgui is installed in your system.
Make ensure the aconnectgui package were installed using the commands given below,
$ sudo dpkg-query -l | grep aconnectgui *
You will get with aconnectgui package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Sound |
| Package | aconnectgui |
| Version | 0.9.0rc2-1-10 |
| Description | graphical ALSA sequencer connection manager |
| Sub Section | Sound |