The REL Strata is very easy to dial in, so is probably an excellent way to go if you do not have experience in setting one up. Problems usually arise when you run the subwoofer level too high because of the "if I paid good money for it, I want to hear it" syndrome. When setting it up, do not just listen to bass instruments. In fact, I focus on how voices and cymbals sound, when dialling it in. Amazingly, even cymbals are improved by a subwoofer, in terms of getting a better balance between leading edge, body of the note, and the decay.
