You need a sub-woofer with equalization, preferably one that calibrates itself. You also need a sub-woofer (or sub-woofer controller) that will put a high-pass on the main speakers.
1) Your room has its fundamental resonance at 47Hz and will have bass increasing below that. Since you're not going to buy a commercial sub-woofer that starts rolling off at that point due to its mechanical parameters you need to deal with the situation electronically to avoid excess low frequency energy.
2) Your room will have horrendous resonances at 57Hz and multiples thereof that give you one-note bass. Notch filters will fix those problems for a single seating position. A higher cross-over (try 120Hz) will move the first resonances out of the main speakers' pass-band so you only need to notch the sub-woofer output.
Forget REL sub-woofers which do neither.
1) Your room has its fundamental resonance at 47Hz and will have bass increasing below that. Since you're not going to buy a commercial sub-woofer that starts rolling off at that point due to its mechanical parameters you need to deal with the situation electronically to avoid excess low frequency energy.
2) Your room will have horrendous resonances at 57Hz and multiples thereof that give you one-note bass. Notch filters will fix those problems for a single seating position. A higher cross-over (try 120Hz) will move the first resonances out of the main speakers' pass-band so you only need to notch the sub-woofer output.
Forget REL sub-woofers which do neither.