The goal of the FRx and HPx is to quiet down engine operation on the fuel side, and smooth out the engine on the oil side.
It does so on the fuel side by giving air an alternative route to exit instead of forcing it through the injectors. Air in fuel causes noise when going through an injector. The FRx routes the aerated fuel back to the tank.
It does so on the oil side because it stabilizes the oil pressure in both rails by connecting them together. This usually does not effect noise, but sometimes helps with the steadiness of idle.
As for your results... It may just be quieter because the parts you installed are doing their job. Our tunes should not be a lot louder than stock anyway. They do increase noise a little bit though because ICP is increased.
Let me know if you have any other questions.