Welcome to the SMD forum!
Just wondering, I could be totally off track, but would my home theatre powered sub box from SVS tuned to 20hz (PB12-NSD - 12" - 400rms) and from measurements on sites is considered SQ/flat/low distortion be put in my car as a test to get a feel for what a more SQ orientated sub would sound like? It would obviously just be temporary with a power cable running to it and RCA's to a sound source and the car not moving anywhere...... The only thing I can think of that might throw it off is that it is tuned to 20hz, but it is apparently flat through the sub range so technically shouldn't be peaking too much at any one frequency? Or is this just not going to work properly in car?
I know this is really subjective, and even harder as I can't really demo the subs before I buy them in my own box and car.....I currently have a Skar VXF tuned low with about 1500rms and it slams hard, SQ seems great, but of course I don't really have anything to compare it with. Big question is, will I will hear a big difference in SQ/more musical spending $400-500+ on a better quality sub say FI Q, SSA ICON, JL W7, Sundow X, DD Audio etc and hear a big difference? Or is this spend more on better quality parts versus a huge change in sound?