If I had to pick one standout ability for this CAP, it's have to be Speed Boost. Speed Boost provides us an incentive to stay in as it lets us accumulate speed increases, contributing to the sweep in letting us outspeed threats. This goes hand-in-hand with how CAP 34 wants to stay in to keep Throat Spray. Unburden does this as well, but the speed increase being tied to the sound move CAP 34 is running puts a lot of pressure on it to click that move as soon as it comes in, Speed Boost in contrast gives you the freedom to do something else and still get the boost. Additionally, Speed Boost appreciates the compression Throat Spray gives it because gives it space to run Protect, as quizel already mentioned. Because of this CAP 34 can also get the Speed Boost much easier than with Unburden, provided it's running Protect.
Now, some people are concerned that a Speed Boost CAP 34 wouldn't run Throat Spray because of the power the ability holds in letting CAP 34 set up for a sweep, however in addition to loving the moveset compression it provides Speed Boost also loves how Throat Spray lets it boost without wearing it down like Life Orb, with that recoil only being made worse by a STAB that lowers it's defense. Additionally given our typing CAP 34 is not going to want to run Specs as its STABs are horrible to be locked into, this also means that even if it didn't mind that it'd want to switch out quite a bit to minimize the damage from being locked into it's STABs, which doesn't gel with Speed Boost requiring it to stay in to get the most of the ability. Additionally, Unburden also has its own issues with potentially running other items. Most notably Grassy Seed, which some would argue still fulfills the concept, but given Grassy Seed is highly used with Unburden, and that we're specifically building for Throat Spray now, I would not. Either way however on Unburden Throat Spray has to compete with Grassy Seed for that item slot, while at a disadvantage. One thing that hasn't been noted about Unburden that should be: Grassy Seed and Unburden work so well because you instantly get the boost as you're sent out, Throat Spray doesn't have this benefit, instead being reliant on clicking our sound move, which as I already mentioned puts pressure on it to do that as soon as it gets out.
Overall both abilities work, but I personally prefer Speed Boost. Despite Unburden's obvious synergy Speed Boost synergizes nicely with Throat Spray in a way Unburden doesn't, making more effective use of it and benefiting more from it, in addition to lacking most of the issues Unburden has.
Now for something quicker, I'm going to show some support for some other abilities already mentioned for the sake of not making another post later.
Dazzling and its clones are nice, not only do they eliminate priority as something we need to worry about but they also help patch up the defense drops from Clanging Scales and make it harder for the foe to pick off CAP 34 after a Clangorous Soul. Very solid, even if it doesn't directly tie into Throat Spray, instead making it easier for CAP 34 to set up and preform its sweep.
Mold Breaker is another one that works nicely here as a way to get past the Unawares and Ting-Lu. While I do believe Clangorous Soul prefers this, it works with both and can be an effective choice either way. Nothing much else to say here.
Now for an ability I really don't like.
Simple is flawed, severely flawed. To get the obvious out of the way, Simple + Clangorous Soul seems like overkill, and not just in the way of it being a massive boost, but also in the sense of +4 being more than CAP 34 realistically needs. Because of this, I feel like it's possible Clangorous Soul Simple sets wouldn't run Throat Spray, they already get a +2 to Sp.Attack, so instead of going all in on offense they could try to use the item slot for other purposes. Even then, Simple still has another issue that this time affects both Soul and non-Soul routes, that being Simple turning that -1 defense drop from Clanging Scales into -2. Already the defense drop hurts us as it opens us up more to revenge-killing but making that a -2 drop makes the issue much worse as we're dropping our defense so much quicker. To me this kills Simple sets without Soul, but even then there's another issue, being Dragon Pulse's significant drop in power from Clanging Scales, sure it works but that's the kind of drop you'll really feel. Even then, that kind ties into the overlying issue. Yes it works, but with how many hurdles we have to jump through to get this in a reasonable spot, is it worth it? Do we want to go with an ability that we need to work so hard to balance, when we can go with an ability that doesn't have nearly as many issues while working better with Throat Spray and overall being a stronger ability? Personally, I don't think it is. Simple simply isn't worth the effort.