Would you choose 1 ou 2 subwoofers for a stereo set?

Do some research into distributed bass arrays. There are numerous discussions on this forum, plus plenty of supporting articles online.

The basic idea is to use 4 or more subs placed asymmetrically around the room to flood the room with the low frequency information. 

The results are amazing.

I run 4 Subs. The 2 on the front wall are in phase. The two on the back wall are out of phase. X’s over at the Subs minimum 50Hz from my Cornwall IV’s.

I use two 15” sealed Rythmik subs in a very difficult room with great results

@markalarsen , Is the E15HP what you have? Are you using it for music listening primarily? (I have been curious about their 15in and 18in sealed models for a bit...Personally have not ventured any bigger than their 12in drivers for music).

For those who can do rudimentary woodworking (just a simple box), the Rythmik Subs are available as DIY kits. For those who can't, a local cabinet maker can do it for you pretty cheaply.

The 15" Rythmik sub comes in a China-sourced 3cu.ft. enclosure, but if going DIY Brian Ding recommends building a 4cu.ft. one, for free increased output.

By the way, the Rythmik plate amps feature the best controls available on the market, far better than most of the competition. Check out the Rythmik website for details.

Two subs or more. I’m using a pair of Rythmik subs,  F12SE-XLR3 and A370XLR3 amp

https://www.rythmikaudio.com/download/XLR3_sealed_quickguide.pdf

I’m  also using a Sublimeacoustic K231 as a 2 way XO. The miniDSP XO sounds promising, especially w/ room correction. I’d I was all digital, I’d be more inclined to pursue it. However, I’m not convinced my LPs would sound as good.