The mod you refer to only changes the gauge, it doesn't change the depth you can go to. If you only install the gauges, the sub is still only using the default crush depth. Use SH3 Crush Depth Changing tool available at the link below to set the depth. (The tool tells you what the official crush depths are listed as for each sub, so you can set each model to official depths if you like).
Download the tool here:
http://www.delraydepot.com/tt/sh3.htm