SUBWOOFER x OVER

The distinction is that the first will pass the signal to your main speakers after extracting the bass below 80Hz which is diverted to the sub while the second passes the full spectrum of signal to your main speakers. This applies only if you connect your main speakers through the sub's connections. Either way, both subs have the ability to filter (remove) the signals above the LP filter setting from being reproduced by the sub.

Which you might choose and what connection options you have (are all these ins/outs speaker or preamp level?) are dependent on what other components you have.

Thanks Kr4,the ins/outs are preamp to amp not speaker.The sub without the highpass filter has no speaker option.

It sounds like to me that the unfiltered high pass is implying that it doesn't implement a crossover for your main speakers. I've found it's best to cross your sub over as low as possible (40hz-60hz) and center your sub in between your speakers. What are the subs your are looking at?