check your HU and make sure your sub output is on then check your rca's on the back of HU I had my rca's to tight one time and was messing with it and pulled the connection out of the HU
of the above listed the RE SX or SE is very nice as well as the FI Q havent heard the bl but it could only be better and ID is also very good but for your price range I would say go with one of the FI subs I hear that TC sounds it very nice but have not heard them personaly
i know a guy that has 2 sx 18's and he's runinn two md3d one on each sub and its the loudest two sub setup I've ever heard he's hittin problably close to 160
well what are you wanting to get 10's 12's 15's well regardless like is said B4 I would go with FI you dont have to get the btl's, hell the SSD's hit hard as **** and they are cheap and the SQ is amazing especialy the lows