The Raritan "SeaEra" has the exact mounting pattern as the Jabsco. If you get the version of it that flushes with pressurized fresh water, it'll be as quiet or quieter than your toilet at home.
The installation is somewhat more complicated than the original installation because you'll have to tap into the pressure water system on the boat, then install the necessary valves and safety devices - but if you want a quiet toilet, you;'ll have to do it anyway. Raw water flushing toilets are noisy; toilets that flush with pressurized fresh water from the ship's onboard system, are quiet.
Jabsco also offers their "quiet flush" series, which is similar to the Raritan unit, and will also require tapping into the pressure water lines on the boat.
So essentially, if you want to stick with raw water, you'll have to put up with the noise. If you're willing to change over to a toilet that uses pressurized fresh water, it'll be a lot quieter. And no, it isn't easy - or cheap - to convert the toilet that is in one configuration, to the other configuration. It can usually be done, but it's always better to buy a toilet that was engineered and designed for the particular application you want.