Eminence makes good pro-audio sound reinforcement speakers, and I haven't been disappointed with the better offerings from JBL and Clarion. I don't have much experience with Jamo and can't comment on those.
If you are comissioning somebody to design and build your subwoofer for you, I would rely on their experience with regard to what woofers work best in their enclosures. Tuning an enclosure for a specific brand and size driver can be a tricky affair, as there is often more to it than simple port diameter, length, and box volume concerns. The type and amount of interior padding, inclusion of baffles or angular diffusers inside, etc., can all make a big difference on the overall sound of your sub.
The key material requirements for a good sub are:
a) Stiff cone. Kevlar reinforced cones are cool, but you can get some pretty stiff fiber-reinforced paper cones for that matter.
b) Quality foam or rubber surround. I prefer rubber, but foam has come a long way over the years, and if kept inside a climate controlled house - has few deterioration problems to worry about. In a car audio sub, I'd stay away from foam if there's any chance of moisture or UV exposure.
Naturally, you'll want to get a sub that matches the specs of the enclosure size you plan on building.
Good luck with your project! DIY speakers are a blast. If I were any good with veneering I'd make my own fronts. =)
As for amplifiers, some people like plate amps - but I'm a fan of the better Crown amps for that sort of thing. The Crown K2 series are really nice, low-noise, and designed for high current applications like driving subwoofers. They're not cheap, however, so if DIY is to save you some money, you're probably not going with the K2-series.
Greg
