I've never really shopped for (or used) 8"s but there's a few options on Crutchfield to compare. For around the same price as the SoloBarics there's these Focals, which I'm sure sound great but won't go as low down in the frequency range. (39Hz vs 28Hz) According to Focal's website they're 214mm (8.4252in) tall on the front face, so they should work for what you're trying to do.
http://www.crutchfield.com/p_091SUBP20F/Focal-Performance-Sub-P-20F.html?tp=111
I saw some JL W7s that looked nice too but upon further review it looks like they wouldn't fit. As always don't buy from Crutchfield if you want the cheapest price, just posted for the sake of checking it out.
http://www.crutchfield.com/p_091SUBP20F/Focal-Performance-Sub-P-20F.html?tp=111
I saw some JL W7s that looked nice too but upon further review it looks like they wouldn't fit. As always don't buy from Crutchfield if you want the cheapest price, just posted for the sake of checking it out.