Apologies on novel fellas. Type fast & got interrupted a few times.
Seems like you are over thinking this. I do it at times hoping the first option meets all expectations. Rarely this is the case. You reach a point in doing research (I do) when you're wasting your time continuing to look. My home theater is a good example, at a certain point I couldn't learn anymore or hear anymore advice which varied from everyone I spoke to. Needed to get some gear in the house to learn what I liked, what I needed. The 45 day return policy at best buy as a something member was very beneficial.
Side note on home audio: While speaking on HT, KEF is what I ended up going with but the best deal I've ever encountered (available to masses) is the Pioneer SP-BS22-LR bookshelves. Good Lord. You won't believe with the price, or size of drivers as I didn't before. At 120 a pair those can hang with anything 3-4 times the price easily. The towers in the same Pioneer line designed by Andrew Jones along with the bookshelves are the only 2 speakers the DIY guys admit they can't make a better one for even twice the price. Everything else they claim they can make better at half the cost which is true in a lot of cases. Markup is typically 300-400% on HT gear.
Amazon does a sale where they let them go at $60/pair & towers for $99/pair. Grabbed 8 of the bookshelves because that's all that was left. If you have an amp in the house and 120$ take my advice and try them. Take them back if you're not satisfied you have 30 days. Just don't let in store display fool you. It's funny how they use blockers so that they the lowest priced appear to output least & slightly increases as u go up to each model that costs more. I digress too much, yet solid info
Go with a 12. Forget the 8' nonsense. Yes there are good 8' yet forget that. How much depth do you have in the area? What are the dimensions on what area you want to put it?
A law from the 70's allows the manufacturers a loophole in using those ridiculous wattage ratings. On receivers in the home they do the same but it's not as egregious as car audio. e.g. ALL AVR's do it with the only exception being Emotiva which makes very good quality power amplifiers, wouldn't want an AVR from them though. The XPA 2 & XPA 5, digress again the quality of music in home audio is just a level you can't reach in the car. Anyways know of a authorized retailer online with prices usually 50% of any other store if anyone is interested in getting into home audio/theater. Wouldn't of mentioned a few months back as I was still completing my setup.
The AVR will be rated at 135 watts per channel. This is only with 2 channels driven, and they don't put that in any description. So 135 per channel is 110 with 5 channels driven, 81 with 7 channels, and so on. If an amp like Boss says 1000 watts it's usually 20% of that.
Aside from the sub you choose the best advice I could give you is to pay the extra 50-100$ for a JL Audio amp. Specifically a Slash or HD, but the XD series is very good as well. The slash was revolutionary when it came out, correct me if I'm wrong but it was the 1st amp that supplied continuous RMS watts. Rated at 500, it always delivered that as long as your voltage remained the same. It usually does unless you have a 600 horse muscle car. They've been at the forefront of the majority of advancements in car audio amps & subs. The JL Fathom that's in the house delivers a quality/level u have to experience. 5-10 acres on each side of the house is required to truly use it though.
If you don't want to spend what a 12w6v2 costs, get a 12' Alpine R series. Then get a JL mono 500 or 1000. When in doubt get more power, in car audio and home audio the manufacturers reps I've spoken with say that the drivers perform best, meaning they are leat likely to be damaged when powered a little over the recommended rating. On a speaker with amp requirements of 20-150 providing 170 watts is where it's least likely to damage opposed to 50 watts where damage occurring is significantly increased. Also, your amp should be strong enough so you don't have to go above 75% gain. People do it all the time, but you shouldn't push you gear that hard. It's your gear, do as u please, you're just shortening the life span when you do.
If u quote me the dimensions and what you're wanting to spend, I'll give you my advice tomorrow. U should have a good idea on what u want. Also want to give u guys a link to a site that's very helpful. Has calculators from correct Wire Gauge to designing box based on driver specs, but it's bookmarked on the laptop.
Alright then fellas. Have a good one