the Sony is actually a pentagon (5 sides, not 6) but i personally would stay away from Xplod... listening to them side by side with other subs of the same size and power they just don't have the same force. i've never been very impressed with any of the car audio sony has put out other than head units.
i have an Audiobahn Alum-10" with a 300watt (2 channel bridged) MTX Thunder ($200) amp in a sealed custom box. i love my sub. it is just as loud as most people with 2 subs yet is still tight and solid. while my sub is Audiobahn's top of the line (it was $450 list) i would imagine that the quality would trickle down.
as for your amp. i would steer clear of the Profile amps. they are a little on the cheap side (quality wise) if you are looking for a solid amp at a reasonable price, check out MTX or US Acoustics. both are very nice.
my suggestion... (from crutchfield)
amp: $129.00
U.S. acoustics USB-2100
300 watts RMS bridged
sub: $149.00
splurge that extra $50 and get this sub. look at the build on this thing... like a rock. much more solid.
Audiobahn AW1000Q
600 watts RMS
frequency response 23-500 Hz
sensitivity 91.1 dB
for the box, i agree get a sealed box. you'll be happy with it, especially space-wise. ($60)
total = $338 (not including wiring)
it's a *little* more expensive. but you get what you pay for. the last thing you want is to skimp on something and then have it go out on you a year later.