Like Zero above says, you can configure your TDA in split power supply mode.
See the datasheet :
https://www.st.com/resource/en/datasheet/cd00000130.pdfBrowse to page 8 and you'll see there example circuit which shows schematic and circuit board layout for mono aplifier with simple power supply.
On page 7. you have example circuit and schematic for split power supply... so you could use your -9v, 0 , +9v power supply
Keep in mind that the TDA2040 chip MUST be heatsinked, as it's only around 60-70% efficient (if you get 10w of audio, it probably dissipates around 2-3 watts as heat)
Also, the maximum audio power will vary depending on input voltage.
Look on page 5 at figure 4 and 6 and you'll see that with +/-9v (or 18v if single power supply), the output power will be around 4w @ 8 ohm and around 7-8w @ 4 ohm
Here's an example amplifier with 2 TDA2050 :
http://www.electronics-lab.com/project/audio-power-amplifier-with-tda2050/You can look at that to make your power supply using a transformer with two secondary windings.... if you want to use transformers. If you want just DC voltage... 9v batteries won't work for long time, they're too lousy (small energy amount, resistance, can not output a lot of current etc)