Well if you want to wait 5 weeks for a sub then get the a2-300. Mind you their customer service has much to be desired.
That's not true at all
Now here is another thing to consider. Just because the specs say it goes to 20hz or whatever for other subs doesn't mean it sounds good doing it. There is a large difference between specs and performance.
Obviously, you've never seen their spec charts and results.
Look at it this way.. You can buy the 8D and if you don't like it you can send it back. They pay for the shipping both ways. A co-worker of mine ordered the a2-300 got disgusted with the customer service he received and then opted for the 8D.
Did he ever even get it? What was wrong? Why didn't he like it? Why would he decide to get a much smaller sub at a more expensive price?
I have the S8 the older line of subs and yes it doesn't hit 20hz, but it produces clean, tight, and powerful base even though mine only has 100 watt amp. The 8D has more power and is much smaller than the a2-300, and I might mention the finish on the Aperion speakers is amazing. You will find it very difficult to buy a sub with its finish and performance for $500. I might also add it has a BASH amplifier in it.
It seems that you're suggesting that the A2-300 has very little power and sub-par performance based on your comments. This is far from the truth.
I challenge anyone in this forum to find better service than what Aperion offers. Yes as you can tell I own these speakers so I know first hand how this company operates. Also I might add if you call them they may have an A-stock 8D for a lower price.
eD's customer service (Chris S. at least) was probably the main reason I decided to go with them. I really want to know why you think their live support, telephone support, and e-mail support just isn't good enough.
Either way you have nothing to lose in trying the 8D first, and if it isn't what you want you can send it back.. Then order whatever other sub which you will have to pay shipping for I might add.
You expect eD to pay for shipping both ways out of their pocket? If the Aperion sub was less than half its price, it may just be worth it. Maybe all that extra money you pay to get an 8" sub goes for the shipping both ways. 
If you didn't like the a2-300 you will have to pay for the shipping back to them and at 72lbs that won't be cheap. So to me it makes more sense to at least try the 8D risk free and actually hear it for yourself rather than take the advice of people who have never heard one. I myself have not heard an 8D either but I will be next week when I go over my co-workers house to check it out. I am sure it will be better than my S8 which does shake the walls in my house.
I don't know of anybody who has ordered an A2-300 and returned it because they didn't like it so free return shipping shouldn't be a reason to look at a sub. If you go with the Aperion just because it has free return shipping, something just isn't right.
Sure, try the Aperion and the eD at the same time and tell me which one is better. Maybe that free return shipping on the Aperion will come in handy.
So the choice is up to you..
Hagar852