One RevBurner will only be able to run one type of gauge at a time. To drive a complete dashboard you will need at least 2 RevBurners and a power supply providing enough power to all components.
A single RevBurner could however drive multiple tachometers(or speedometers) at the same time. Just not both types at once. You'd have to provide enough power for all gauges, which I doubt the onboard regulator can handle, so you'll need to connect the gauges directly to an external power supply.
Another problem with this setup is the inability to calibrate each gauge individually. With the same number of pulses, you could get different RPM or speed readouts on multiple gauges.
There is a schematic for connecting multiple RevBurners to a dash using a single power supply
hidden away hereI did have some trouble finding the schematic, as there's both a documentation section and an FAQ containing only the power supply info. Cristiano, could these be grouped together?