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If I recall correctly, the stock base system runs the speakers at 4 ohms. However, the UHFS system adds a subwoofer, an extra amp, and uses 2 ohm speakers.
Some folks have swapped the base system front door speakers with those from the UHFS and claim the 2 ohm speakers improve the sound. You'll want to get the speaker mounts from the UHFS to swap onto the base front door or you'll need to make your own brackets since the speaker size is slightly different. No word on if running 2 ohms increases the heat generated wherever the amplifier is (I assume it's at the MCU), but I'd imagine that more heat would come with less resistance.