You know Dan, I don't know if you'll notice any big differences as far as sq goes with this plan, but I get what you're going for. Are you handy with tools and a little bit of wood working? I think you're a great candidate for diy. Just keep the SVS' while you work on your project until it's done. Take your time with it and have some fun.
I suggest this because I'm noticing that you seem to get bored every couple months and look for more stuff to upgrade. I think building your own would be more satisfying, and you'd be more inclined to want to keep them, having built them yourself.
I would except for a couple reasons
1 I suck at building stuff absolutely suck
2 my job Is very intense I just don't have the energy when I'm out of work
3 I need very nice looking passive subs RBH fits that bill they look better then the SVS
And finally after experiencing the RBH I own already a few of those will be my forever subs
The 1212 PR smashes both SVS PB 4000's combined it'll outperform the PB 16 so 3 to 4 of those in the theater will be all I want
The theater room will be end game moves my next speakers will be my last in that room it's between JTR and JBL that won't happen for a bit though I love the Studio 5's
Where your really spot on with that assessment is my other system in the bedroom but it's not really boredom
I just like flipping stuff and experiencing something new I only have so much time in life as do we all and my ears aren't getting any younger so I want to hear as many speakers and gear as I can