An often overlooked Catch-22 was mentioned by teo_audio, and I want to make sure it's not missed by the OP:
>> make the bass sound good -inside of that cistern. <<
Plainly speaking, solving one problem (sound transfer) significantly worsens another (acoustics within the room), particularly in the bass. Since this is a home-theater project, the processor will probably have DSP, which will help. Still, the more successful the isolation is, the more that bass trapping will become an absolute necessity.
>> make the bass sound good -inside of that cistern. <<
Plainly speaking, solving one problem (sound transfer) significantly worsens another (acoustics within the room), particularly in the bass. Since this is a home-theater project, the processor will probably have DSP, which will help. Still, the more successful the isolation is, the more that bass trapping will become an absolute necessity.