Feel free. An unfettered debate is a healthy one! Sorry that it's off topic, but the guy hasn't made a separate post yet asking his question, so...
Let's make some real comparisons for the sake of argument. This setups include currently available parts at the best prices I'm able to find in a reasonable search right now:
DIY setup to compare to a single JTR Captivator S2:
#1 Single boxes
Drivers $1000 - 2x Fi Q-18 w/ options OR SSA Xcon-18
Amp $800 - CV-5000, bridged mono
Cabinet $200+ - BB, dual opposed or front facing, magnetic grilles, cabling, Duratex, etc.
DSP $175 - MiniDSP 2x4 balanced + 2.1 adv. plugin
Total $2175+, slightly less output compared to S2. Lots of additional work to build the cabinet and do the DSP. No single-source warranty.
72.5% of the cost of an S2, but a ton more hassle and time.
If you don't want to build the cabinet, you might soon be able to buy an Assemble It Yourself (AIY) dual-opposed cabinet from Erich at DIY Sound Group for around the same $200, but it won't include grilles, and will still require you to have clamps and/or brad nailer.
#2 Multiple boxes
Drivers $900 - 4x Obsidian Audio 18-d2 (only value 18" I can find)
Amp $800 - same
Cabinets $200+ - 4x Chinese Birch, magnetic grilles, cabling, Duratex, etc.
DSP $175 - same
Total $2075+, likely slightly less output than the S2, but potentially better room mode smoothing. Lots & lots of additional work to build the cabinet and do the DSP. No single-source warranty.
69.2% of the costof an S2, but way, way more hassle and time.
If you wanted to AIY, with flat packs from Erich, they could be had for ~$170/ea incl. shipping, cabling, glue, connectors, Duratex, etc. That reduces the value, removes magnetic grilles, but also reduces the time and hassle.
If you want to increase that to 8x, basically double the cost and many more hours of assembly. That far exceeds the S2 in price, but would prolly give ~60% more performance, too, with the real world output of the CV-5000.
Switching to 15" drivers poses an even worse price/performance ratio than the 18s, generally. Also, remember that each of these DIY/AIY solutions has the multiple drawbacks I pointed out earlier.
The point is not to trash DIY, as I'm a firm believer in it. It's more to point out the extremely high value of the Captivator S2!