Does a custom profile increase gamut?
In general, yes. The generic profiles supplied with a printer are usually quite conservative and don’t use the full gamut of your inks. Using a custom profile for your printer/paper/ink combination you will usually find better shadow rendering and a more neutral output. However a profile cannot perform miracles, you are still limited to the gamut provided by the ink that you are using. For example inks are generally poor at rendering some intense colours, noteably blues or greens.
