I'm not convinced I need high pass filter since I plan to use my amp sub out which will send an LFE signal out so I'm counting on it do deal with the cross-over
You're mixing up some things I think:
- HIGHpass is to cut the bass out of your main speakers, so they don't overload. If right now you can play blasting at full volume and it sounds OK to you, fine. Otherwise if your main speakers are straining, you
need a highpass filter, because otherwise adding the sub will make more boom with the main speakers' distortions still going on = not good.
- Do NOT assume a "sub out" means the highpass is being "dealt with" inside the amp. A number of two channel units very STUPIDLY have a sub out with no highpass at all.
- Also stupidly, sometimes they do but it is not mentioned in the manual-Onkyo, maybe Yamaha too. I remember one thread where an owner said if you engaged the YPAO on whatever model that was, you could set highpass. Not documented.
- Meanwhile the lowpass cuts the highs out of the sub so you don't hear voices coming from the floor or whatever.
- LFE = Low Frequency Effects. This is a specific channel for movies, it is NOT the same as "routing all the bass to the sub"-the other If you use your "sub out" I don't think you need to worry about this.
As for the sub, life really begins at 12" and 300 or more like 500 watts. In a more modest space and system, maybe a ported 10" or exceptional sealed 10. At one extreme I got my brother this
https://www.monoprice.com/Product?p_id=9723
which really does not have enough power, but in his system adding nice lows up to fairly loud SPL. There is similar from Parts Express, which probably not available for you either. Can you get Polk? They also offer something similar.
But if you can save, it's better. I just put an SVS SB-3000, wow super well thought out and a ton of low bass with a lot of SPL possible. I don't think you need that much for your situation but I'd try and save up for their 1000 series. Used is also fine BUT not like 10 years old stuff, electronics can break.