I'd change the 10k output pot to 50k or 100k for gobs more output myself.
There is a different fix in the build notes of the aion project. It also adds a charge pump for an 18v switch
"Increased volume
The stock SM-9 is known for having low volume. There are two confusing and easily-remedied design
decisions causing this.
• R19, the 4.7k bias resistor for IC3A, cuts the signal in half when combined with R18.
• R27, the 10k resistor in series with the volume control, halves the maximum volume again.
We have corrected both of these in the default parts list for this project, raising R19 to 100k and
recommending to jumper R27. With these two changes, the maximum volume is comparable to other
distortion effects."