Hi All, I am currently looking to upgrade my two Audioque HDS3.1 (probably 4-5 years old or so, but still in good condition) which is currently paired with a SKAR SK-2500. They sound great but I am looking for deeper and lower bass so I was considering getting just one large sub (a 15" or 18"). I currently have a car audio battery so I think I have enough power and have just recently understood that more cone surface area equals deeper and fatter bass. I currently have a 2003 Lexus GS300 so probably will lay it in the trunk. I think the amplifier is pretty good unless any of you have any different opinions, I am very open to hearing about it. Thank you all! Currently, these are the subwoofers I was considering upgrading to, let me know what your thoughts are: - Audioque HDC4.115 or HDC4.118 https://soundqubed.com/product-category/subwoofers/hdc4-0/ - Audioque HDC3.115 or HDC3.118 (Might be too underpowered, what do you think?) https://soundqubed.com/product-category/subwoofers/hdc3-1/ - SSA XCON 15" 2000w or XCON 18" 2000w Subs - SHOP BY BRAND - SoundSolutionsAudio - XCON - SSA STORE - SSA ZCON 15" 2000w or ZCON 18" 2000w Subs - SHOP BY BRAND - SoundSolutionsAudio - ZCON - SSA STORE - I am guessing that SSA ICON's are very rare and hard to find currently, I previously owned DCONs so I think that SSA produces really quality subwoofers. The DCONs were just a little too underpowered for my taste. Not sure if XCON would be suitable either. - Sundown Audio SA Series (Might also be underpowered?) SA SERIES - Any of your suggestions? My Amplifier: SKAR SK-2500-1.D https://www.skaraudio.com/products/sk-2500-1d Thank you to all who can help, much appreciated!!