Best case scenario with Sony amps is that you get half the power they are rated for, and quite often less then that.
Also for the above statements about boxes to be true, they have to be properly sized, and good quality.
An improperly sized sealed box will sound worse then a properly built (for the subs) ported box, and vie versa.
If you are getting someone that really knows how to build a box (do all the calculations and such), you can get a very good sounding ported box.
I used to run a sealed box, but had my friend build me (I forget what its called, 6th order bandpass or something like that, its where the two subs face each other in a push-pull configuration), and the difference was unbelievable.
Not only was it louder, but it hit lower frequencies, and sounded better.
Now in my case the sealed box wasn't that great quality, so I don't know what the comparison would be to a quality sealed box, but the type of box, and more importantly the actual design and build quality of the box can make all the difference to how your subs sound.