Anthony, I'm assuming that the reason is that it's probably (I don't know this for sure) a very inexpensive receiver. Either that, or it's got a few years under it's belt. Either way, that is merely what the receiver is rated at. It may actually extend a little lower. You'll only know for...
The XO bypass switch is only useful when you have a receiver or pre/pro that has a XO built in for the sub. It's best if it's a 4th order (24dB/octave) at 80Hz or lower. If your receiver doesn't have a XO for the sub then set the sub amp's XO somewhere around 80-100Hz. You don't want it higher...
Anthony, What do you want to know that we haven't already told you in the DIY forum? It's frequency response, I'm assuming you're more concerned about it's low frequency response, is completely dependent on the enclosure it's put in. In general though, the lower end is usually somewhat...