The Fi X series is just underutilized, and severely so. SSA has the same problem with the DCON and I would suppose even the GCON as well and I'm certain that Incriminator sees the same issues with their two lower powered lines. For some reason everyone thinks they have to have at least 3kw of subs and amps to make a good and loud setup and it's just so far from the truth. My sister's single 12" DCON on ~500watts sounds impressively good, can rattle your teeth just fine, and didn't cost an arm and a leg to pick up. It didn't need $1K in electrical upgrades (none actually) and it gets loud enough, even for me. The Fi X's are targeted toward people who for whatever reason are limited to running in the 500-800 wrms per sub power range. While they can handle more, especially so with the BP option, pushing power levels to them that far over their rating bring the user to the point that the SSD's become the next logical step up and the price difference reflects that, IMO. The X is the more budget oriented line. It's a great sub in it's own right but not quite up on the same level as the SSD. While both are for daily listening setups, both have triple progressive spider packs, both are 3" voice coils, and both have cooling options, the size and configuration of the motors plays to the subtle fact that the SSD will have an edge in output. Neither are going to disappoint though so you/your customer can buy with confidence they're getting a great sub.