Basically, reflex loading has a tuned chamber on one side of the driver (irrelevenat which way driver is, other than for box volume taken up/not taken up by driver - as Steve said) which is usually tuned for the lowest frequency the cab can play before the driver becomes unloaded (the air stops giving the driver mechanical cushioning leading to over excursion or 'bottoming out' where the voice coil former hits the magnet).
A bandpass cab has 2 chambers, front and rear which are tuned for different frequencies (6th order bandpass), one lower, one higher (or one a sealed chamber - 4th order bandpass). This allows slightly higher output but generally over a narrower bandwidth, and needs a fairly robust driver as there is less mechanical suspension in this type of cab and it's easier to break drivers as you can't hear them bottoming out because they're hidden away in the box.
Here's a plot of one of my BP6 cabs and you can clearly see how it only performs between 2 very distinct tuning frequencies:
In the KSS pics i'd say (imo) it's debatable whether the angle actually offers any sort of front chamber loading due to the narrow angle, it's very hard to measure these things - often it's done to reduce the frontal size of the cab (like Noise Control Audio).
Here's the aforementioned BP6 cab, which is more of what is known as a manifold design, where the whole open area in the centre acts as a port. you can really feel the effect of the port when you're in front of it.
Horn loading doesn't neccessarily give better throw, it's more to do with the fact that they have higher sensitivity to begin with so can achieve higher SPL's which means the sound travels further. There's also a funny thing to do with how the inverse square rule changes or something but you're better googling for that......
And i haven't said it yet, but will say it here, the Opus rig at the forum party was very nice sounding indeed, those 15" bass bins are proof that you don't need to go for large format drivers to go low and loud.
