Gen 3 Navi w/ separate Amp sub/Amp installation

Good Day everyone ,

i have a 2010 Gen 3 prius with a navi and separate passenger amp , i am trying to install an Alpine SWE-815 active subwoofer , i should support High level and RCA , i tried connecting to the rear speakers , however it sounds very shallow for what it should sound , i tried to also connect it to the front speakers but also the same issue , should i connect it to the pre-amp signal or what do you think the issue is ?

Thank you