whats the best way to wire my subwoofer to my surround sound.

Hi, I'm new here and was hoping someone could answer a question I have about speakers. I have some old hand me down speakers. They are big and tall but they sound great. I don't have surround sound speakers so I'm looking for some. DO they need to "match" the older speakers I have to sound good? Do I need to buy the same brand?

I have some old office speakers Altas
FA138T167 that I would like to try with my home receiver, I can just bypass the transformer and they work O.K. but these also have a crossover on them should I run my signal through the crossover if anyone is familiar with these what wire + or - should I connect to the Green and Brown wires going to the crossover?

On a trip to Lowe's a while back, I came across a display of Onsia's flat-panel speakers. The display wasn't terribly informative since they didn't let you choose to listen to one speaker over the others, but I really loved the idea of completely hiding my home theater speaker system, and perhaps my entire home audio system, in the walls. They have three types of speakers: In-wall, which can handle 50W RMS, and in-ceiling and in-frame, which can each handle 25W RMS.

I was wondering if anyone has had experience with installing/listening to these (or perhaps more generically with NXT audio technology in general), and what your impressions are.

This thing is probably 20 years old, 15" sub in an end table type enclosure, I bought it with a SAE Amp from Crutchfield. My question is: why are there 5watt 8 ohm ceramic square non conductive? resistors across the speaker terminals? I assume this was to limit the output signal as this sub was passive and you could connect your front speakers and the sub all from one stereo channel. Do you think that's what they are for?
P.S.
How many Watts do you think I should look for in a new Amp to power a sub that size?
Thanks