The Aztech Sound Galaxy NX II is a 8 bit sound card and compatible to
Sound Blaster 2
Playback 44.1 kHz, 8 Bit, Mono
Recording 22 kHz, 8 Bit, Mono, Line-In is Stereo, Mic-In in mono and has auto-gain-control
Adlib - OPL2 YM3812
Disney Sound Source
Covox Speech Thing
Supports Auto-Init DMA, hardware ADPCM decompression
integrated 4 Watt amplifier
dynamic filter between 4 kHz and 23 kHz
integrated analog mixer for Line-In / Mic-In / Line-Out / FM / CD-In / PC-Speaker-In
external volume potentiometer
Bass/Treble/Balance controls
Game-Port
CD-ROM connector with modified AT-bus interface
Resource setting by EEPROM.

Image of the card: http://mail.lipsia.de/~enigma/neu/pics/cps_sb2.5.jpg
It was also sold in Germany by CPS Hamburg as Sound Blaster 2.5 with different software.

The software consists of two disks, available at the Aztech ftp f.e.
ftp://www.aztech.com.sg/Support/DOWNLOAD/sg/NXII/
The disks are in two zip files: NX211-1.ZIP and NX211-2.ZIP
Running install.exe starts the installation. The installer requires the files to be present on drive A:.
The installer detects the card and then asks for a folder name on hdd. After the files are copied the installer sets the resources in the cards EEPROM. Then it runs Demo.exe which fails to detect the card since the resource setting removes the card from the system.
After the installer finishes you have to power off the system (no coldboot but real power OFF), best wait some time then power on again. Now the card is available at the set resources.
The Power Off is always required after a resource change.
The installer adds to the autoexec.bat two environment variables:
SET BLASTER=A220 I5 D1 T2
SET SOUND=C:\SGNXII
where SGNXII is the installation folder.

Let's go through the software:

On the left side are the components and on the right side the utilities.

INSTATCD

The Install AT CD utility allows to choose the operation mode of the CD-ROM connector and adds the driver lines to config.sys and autoexec.bat.
This is a pretty nice feature, since you just have one connector and set the type of CD-ROM used by software.

AZSETUP and NX2VOL are tools for Windows 3.1

DEMO.EXE plays a digitized file and at the same time a FM song for functional test of the card
DEMOFM.EXE plays just a FM song

SG2.EXE

This tool is the diagnose tool for the NX 2, it detects the card and allows to test each part separately.

SP is for Covox Speech Thing and SS for Disney Sound Source

SGCOX.EXE

This tool allows to enable and disable Covox and Sound Source support.

SGFIG.EXE

SGFIG allows to set the hardware settings, incl. CD-ROM connector mode. Please remember to Power Off the system afterwards.

SGTSR.EXE

SGTSR is a resident tool that pops up a textmode control to set volume/balance/bass and treble. It can be unloaded.

SGVOL.EXE

This is the command line tool for volume, balance, bass and treble.

Drivers Folder

Here are the CD-ROM drivers for config.sys and the Voyetra Media Player with different API modules that is used by some other programs.

Windows Folder

Just the driver for Windows 3.1

Voyetra Folder

There are programs from the company Voyetra, two windows 3.1 programs, the Jukebox and WinDAT which is a basic WAV tool.
In the SONGS and SOUNDS folders are Midi files and WAV files.
Interesting is the SSCRIPT folder that contains the Voyetra Sound Script Interpreter (Version 0.92). The interpreter allows to write a text file with commands to play FLI animations and sound/music with the Voyetra Media Player at the same time. Here are some impressions how the batch file loads the modules and how the script looks:

The STRACKS folder

The Soundtracks folder contains a the SONG.EXE TSR that allows with the help of the Voyetra Media Player to play music in the background, incl. playlist support.

It is not really optimized for a small memory footprint, but it can be unloaded completely afterwards.

GMASTER folder

This folder contains the Galaxy Master NX2 program which is a basic editor for digitized sound.

It allows to load and record VOCs, effects like Echo, Fade, Pitch, can be applied and also additional VOCs mixed with the current one.

Some note on the Sound Blaster 2.5 package by CPS. The SB 2.5 is a SG NX II with a sticker on the main chip and some green color on the board label. The basic software package is in some aspects (surprisingly?) similar.
There is a program SBTEST.EXE which looks like SG2.EXE just "SOUND GALAXY" is "SOUND BLASTER" and the copyright is changed to CPS Hamburg. The main difference is that there are no lines for SP and SS test. That the card is compatible with Covox Speech Thing and Disney Sound Source is also not mentioned in the manual anywhere.
There is a program SBFIG.EXE which looks like SGFIG.EXE...
There is a program SB2TSR.EXE which looks like SGTSR.EXE...
There is a program SBVOL.EXE which looks like SGVOL.EXE...
There is a Sound Track program SONG.EXE that can play *.CMF files from a playlist in background and can be unloaded by SONG /Q
Even the command line parameters are the same.
And finally there is a Windows 3.1 program called WSB2VOL for volume control, that looks like...

The installer adds SET BLASTER=A220 I5 D1 T3 to the autoexec.bat.

Well, the SB2.5 package has also some non-specific programs that are different:
Talking Blaster which is a Reciter for german text
The Demo of the FM/Midi sequenzer program Allegro.
VOC386 Pro V2.0 an editor for VOC files.
A CD with a no-save version of the Multimedia presentation creation program HSC-Interactive and a bunch of VOC files and images.

The manual has a page with the electrical specification of the CD-ROM interface and Game Port.