Not sure I understand the objection, but I don't think that's a point being missed.
The OP's idea involves potentially having a signal below 8Hz, "using a second channel/amp/cab with my signal going through an octave doubler." Without even going into the context that was intended, in general terms, what I'm reading in many of the replies is simply that there are impossible and impractical aspects to the idea. Just dealing with the "cab" and the possibility of that, not practicality, no bass cabinet can do this, no standard subwoofer can do this, servo-driven subwoofers may go down to 16Hz (so can't do it), systems than can do this are not "cabinets" but are built into rooms where they are installed (possible but not a cabinet).
The fact that "you feel the bass" isn't relevant to the question of whether you can use a second channel/amp/cab going through an octave doubler and produce subsonics down to below 8Hz.
This video is discussing a different question, but it hits on some of this in an interesting way...