Best Way four Bass Array

I have heard DBA, Distributed Bass Arrays in two home systems

that both qualify as " Best Home Sound" I have heard. I have not

been in every high end home system but I have experienced some

pretty good ones. 

Here is the outline of what I consider as key features:

1. Four Passive 8" subwoofers.

2. Powered by a separate 500+watt amp.

3. Must have fully adjustable phase control. 0-180 won't do.

4. Sealed boxes for a fast, tight sound.

5. Down firing preferred.

Sadly This eliminates the one newer Sub I own. REL T5 x as it does not have the required type of phase adjustment control. Also powered.

Readers that have been down this path, please give me a Brand to consider. 

I want this to be a $3-4k adventure. Buying used is best.

If you do not subscribe to this bass system, I understand. Please start your

new counter thread rather than pollute here.

Thanks!