FWIW I have an Arendal 1723 1s. I use it in my modest 5,1 HT. It is a fantastic sub, two for music would fit you very well. I consider them the equivalent to an SVS SB 4000-in specs. They have a 45 day audition period. You had mentioned it on your list of candidates.
Musical subwoofer under $2000
I’m looking for advice on what vendors to look at as l’d really like to add a subwoofer to my 2 channel setup. The room is c. 30x15 feet or 42 square meters with low ceiling of about 7.5 feet or 2.2 meters. Budget is c.$2,000 and my 2 channel speakers are Sonus Faber Sonetto VIII. My amp offers pre-out connection. I’d like REL but their S range is now too expensive, so something close in musicality would be great.