REL subwoofer selection T5 T3 or R series

Or would you suggest another sub. Looking for something sealed, compact, and under 5-6 hundred.

The T series is designed for home theater, not music. The lowest crossover point is too high for music use in the opinion of myself and reviews I have read. I have 4 pairs and one single sub and appreciate what they can do but doubt that you can find something you will be satisfied with is the price range you mention. I would look for a used REL Strata or Storm; I am not sure if they are sealed or not. My 2 Stadium ones are ported and my Storm is at a friends. Remember, low bass is the hardest part of the audio spectrum to reproduce; sending a boy to do a man's job will in the end be a waste of money. I doubt that in the price range you mention you will find something that significantly improves the performance of your main speakers. There use to be a saying in auto racing" nothing beats cubic inches but rectangular money", meaning it always costs more to get the same performance out of a smaller design.

The Strata III is not ported like the Storm and Stadiums are. Many REL fans like the Strata III in smaller rooms since they feel it's faster than the ported models are.

My REL Q150E might bt too old to mention...but I guess I just did. Another one just sold on Ebay so I guess they're around....they sound amazing...10" sealed MOSFET front firing...fast and sweet, inexpensive.