Re: Beyond the towers (hear me out)
If this were me, I'd probably just put the Sierra 2's on Isoacoustics Desk Stands, that way the stereo image and soundstage will always be on point and right at ear level. The other option is to get tall, adjustable speaker stands (like the ones meant for studios and the like) and have the speakers in front of the desk, on the stands, adjusted above the monitors, and pointing down. Or just ceiling mount them, especially if your ceiling isn't that tall. Lots of options for ya.
I think your GIK ideas with panels are fantastic. I can never make up my mind between Acoustimac and GIK, but I'll probably go with Acoustimac because their panels are cheaper since they don't have the built in gap in the panel for flush mounting, they use their "Z-Bar" hangers instead that give it some space from the wall. GIK has those scatter plates, though, which looks really darn cool. Decisions, decisions.
As far as separates, I'm just a Schiit fan boy and I'd personally wait to buy a whole chain from them, since the preamps are coming out soon and the amp sometime next year. The NuPrime amp looks great though, I know a few guys with NuPrime gear and they are huge fans of it as well. The Schiit amp is going to be pretty power hungry and inefficient, so probably will run hot as well, whereas the NuPrime gear won't do that. There are not a lot of affordable preamps out there, most are in the thousands of dollars for no good reason. The Schiit preamps that are coming out are literally the only ones I've seen that come in at a reasonable price for the feature set. If you find one that is reasonable, let me know.
The only preamp currently available that provides real value, to me, is the Emotiva XSP-1, but it's still $1k, and the DAC isn't as great as the Schiit Multibit DACs, but still good, and you can also bypass the DAC with one of the inputs on it. It also has a phono preamp and (best feature of all) extremely good subwoofer management that would negate the need for the miniDSP 2x4, which, while great, is limited in sample rate and bit depth. If you're placing the speakers near-field, I doubt you'd need the room correction anyway, just the low pass filter. Plug the Bifrost and amp into it and you're good to go. Still, you'd be paying more for the preamp than the rest of the signal chain, and that just doesn't make a single bit of sense to me.
It's just incredible that there aren't ANY affordable preamps out there until Schiit releases theirs. There are plenty of great/affordable integrated amps, but preamps are so very rare.
-Alex
PS4/Nvidia Shield --> Emotiva XMC-1 --> Emotiva XPA-5 --> Ascend Acoustics Sierra Towers and Horizon Center w/ RAAL tweeters (L/C/R), HTM-200 SE (Surrounds), 2x Rythmik F12 subwoofers