Subwoofer Class A/B vs D Power Amplifier

The REL T5 is great for a small room. They are so good and blend so well that you don’t need to use 4 of them. One is fine, two is better, but it depends on your music.

The JL will likely overwhelm a small room.

I like to keep amp classes both Class AB, but that is a personal preference, similar to how I like paper cones more than aluminum cones. 

I have absolutly no doubt, within the first ten seconds your choice will be obvious. The only difficulty may be finding a dealer who carries both brands. 

Dear @vta2005 : First than all the units you named are not subwoofers so the amplifier is not an important issue.

The Rel goes down to 32hz at -6db and this means that probably you can't get bass at no lower bass range of 45hz.

The JL is alittle better on that regards with a spec of -3 db at 29hz but no one is a subwoofer.
 A subwoofer must goes down below 20hz, not at 20hz as many of us could thing.

So, look at JL other model and don't be to worried about the amp design when is more important the subwoofer overall design and its quality levelexcecution of that design.
No, you don't need 3-4 subs in your room. As a fact no one needs it in a home system to listen MUSIC no matters what.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.