I run two SVS SB4000 in my HT room and know the sound very well. I don’t think they would be ideal in a 2 Chanel setup. I don’t think they will have enough speed and you will wind up with bass overhang that muddies the two Chanel system. I think for your usage I would go for the REL.
Also, as soon as possible start saving for a matching second sub. If you truly want them to disappear that is the way to go. Good luck and cheers.