Hi there "AerialView", and welcome!
I'm not quite sure what you are describing! In some places it sounds like a fully-coupled two-leaf ("All walls are double stud, 25 gauge, 24" OC with double layer 5/8" per side with batt insulation") which wouldn't be very good for isolation, but other places sound like the walls aren't built that way at all: ("The building is Cinder Block"), while yet other places sound like there is some attempt at partially decoupling something ("to do hat channel (25 gauge), resilient channel and then 2 layers of 5/8" rock")! So it's hard to understand what you really have there. Also, ith the latter comment, it isn't clear why you would have both hat channel AND resilient channel on the same wall. For what purpose?
Am I creating a triple leaf design by adding another cavity between the sheetrock and the spancrete
What spancrete? Where did that come from?
2. Is the resilient channel counter-effective in this scenario even though the likelihood of short-circuiting is incredibly low
Short-circuiting what to what? The purpose of resilient channel is not to prevent flanking (short-circuiting): it is meant to decouple the drywall from the studs, joists, trusses or whatever else it is attached to. If the inner-leaf drywall would otherwise be attached to something that is connected to the outer-leaf, then yes, you need the resilient channel. But from your description it isn't clear what is attached to what!
I'm concerned about Low Freq through the floor.
Why? How is that related to the drywall on the walls and ceiling? I don't see the connection. You said your floor is "poured concrete foundation", which I assumed to mean slab on grade. Is that not the case? Is there some type of crawl space below the floor slab? Another room down there? Is that why you are concerned about low frequency transmission through the floor?
3. Dependant on answer to question #1, would RSIC-1 Clips or similar make a significant enough impact on the design to make it worth the cost?
If you are already using resilient channel, then why would you also want RSIC clips? They both accomplish the same purpose, and you cannot even use resilient channel on RSIC clips. RSIC is meant to carry hat channel, not resilient channel, which is very different.
Would they be reliable fastened to a precast concrete ceiling?
You should probably take a close look at IR-586 to see why that would be a terrible idea. Putting drywall directly over a massive surface with only a very thin air gap is a really, really bad idea, even if you do use RSIC clips plus hat channel, or resilient channel. If you look at the graphs on page 8, you'll see that with this scenario, the entire low end of the spectrum has even WORSE isolation than for just bare concrete! In other words, doing what you propose (adding RSIC clips plus hat channel then drywall) directly on the ceiling surface, you would LOSE several dB of isolation for every single frequency below about 350 Hz. Meaning the entire low end of the spectrum, plus the first octave of the mid range. All of that would have worse isolation than if you did nothing.
If you look at the subsequent pages, you'll notice that there are many, many ways to get the same effect (reduced low frequency isolation) and very few ways to get an increase.
Please post some photos of what you actually have right now, and some accurate diagrams of what you plan to do, since it isn't clear what you have in mind, and if it is what it sounds like, then you'd be making things worse, not better.
- Stuart -