I researched both REL and Rythmic. I think either one is a good choice, but I think the high level connection designed by REL is genius. The high level connection allows the subwoofers to play more like woofers. The key is calibrate then to not play too loud. If you can detect them you either have the volume turned up too high or you need to calibrate the crossovers to blend seemlessly.
I have a pair of Paradigm Prestige 85F towers. Originally, I was going to buy a pair of REL T9i"s, but went with a pair of REL S3 SHO's. Glad I went with the S3's. No matter what you decide, go with a pair. Much better sound than just one. I would not get anything smaller than the REL t9i's. Right now playing two bookshelf speakers is lacking an enormous amount of bass. You could also purchase towers unless you have a space limitation. If you are limited in space and have to settle for bookshelf's, spring for a pair of the REL S2 SHO's. I can put you in touch with someone who can surprise you with a great price. This was how I could afford the REL S2's.
I have a pair of Paradigm Prestige 85F towers. Originally, I was going to buy a pair of REL T9i"s, but went with a pair of REL S3 SHO's. Glad I went with the S3's. No matter what you decide, go with a pair. Much better sound than just one. I would not get anything smaller than the REL t9i's. Right now playing two bookshelf speakers is lacking an enormous amount of bass. You could also purchase towers unless you have a space limitation. If you are limited in space and have to settle for bookshelf's, spring for a pair of the REL S2 SHO's. I can put you in touch with someone who can surprise you with a great price. This was how I could afford the REL S2's.