I have a vintage Velodyne DD18 subwoofer that just died. 
Its prodigious 18" cone and 1,250 watt digital servo controlled output was clean (like 2% distortion) down to 15 hz or below. At 120 lbs, it's a monster and understandably provided amazing deep LFE in my 18' x 27' x 9' room. (4,400 cu ft). But it's dead and cannot be repaired. The DSP board died and those famously are impossible to repair.
Aside from the weight and size, there is one major drawback to the DD18: With just one sub I did have a mode problem, even after using REW and Velodyne's sophisticated DSP system. I am only interested in listening to music and I love to feel that slam in my guts. And I do like to play loud on occasion, especially for parties.
So I have a few options and I'd appreciate some expert help in deciding what to do:
1. Buy a replacement plate amp/board from Velodyne and I'm back to where I was. Cost about $2,500 but just guessing. https://www.audioholics.com/subwoofer-reviews/velodyne-dd-18
2. Buy 2 SVS-2000 Pro subs - 12" aluminum cone/1,500 watts. They don't go as low (still maybe 18 Hz?) or have digital servo but have a good app for integration and with 2 subs would help the mode problem. Cost $1,710 before negotiation. https://www.svsound.com/products/sb-2000-pro
3. Buy 2 Rythmik L12 subs - 12" paper cone/smaller amp not comparably reported. Has digital servo control so easily down to 15 Hz and very low distortion, but no sophisticated DSP for integration. Cost $1,320 https://www.rythmikaudio.com/L12.html https://www.audiosciencereview.com/forum/index.php?threads/rythmik-l12-subwoofer-review.12140/
4. Other ideas?

Aside from the weight and size, there is one major drawback to the DD18: With just one sub I did have a mode problem, even after using REW and Velodyne's sophisticated DSP system. I am only interested in listening to music and I love to feel that slam in my guts. And I do like to play loud on occasion, especially for parties.
So I have a few options and I'd appreciate some expert help in deciding what to do:
1. Buy a replacement plate amp/board from Velodyne and I'm back to where I was. Cost about $2,500 but just guessing. https://www.audioholics.com/subwoofer-reviews/velodyne-dd-18
2. Buy 2 SVS-2000 Pro subs - 12" aluminum cone/1,500 watts. They don't go as low (still maybe 18 Hz?) or have digital servo but have a good app for integration and with 2 subs would help the mode problem. Cost $1,710 before negotiation. https://www.svsound.com/products/sb-2000-pro
3. Buy 2 Rythmik L12 subs - 12" paper cone/smaller amp not comparably reported. Has digital servo control so easily down to 15 Hz and very low distortion, but no sophisticated DSP for integration. Cost $1,320 https://www.rythmikaudio.com/L12.html https://www.audiosciencereview.com/forum/index.php?threads/rythmik-l12-subwoofer-review.12140/
4. Other ideas?