Yeah you're dealing with differnt issues with speakers designed like that.
The basic "layman's" answer to all of this is that the IV's will do better set up in large spaces, or where at the very least they're on the "Long wall"!(where you can get the speakers spaced further apart!
Yes these speakers have the potential(set up right) to have very smooth, fast, well balanced bass with the Dual woofer Dappolito design(not to mention 1st order cross, multiple driver array). One woofer might balance out the other on the speaker, placed on a "different plane" in space. Still, in small room settings, or where they're not more "optimally set up", you'll have comb filtering issues, boundary to woofer cancelation/reinforcement issues(compounded with multiple woofs on the same planes), and other compouned issues. Sitting at "tweeter level" with your ears is also more critical in regards to comb filtering here as well. That said, stick these speakers in a room where the woofers and walls/boundaries are spaced at distances which are multiples of each other, as well as the listening distance, and you can easily have holes and peaks that will pronounce the problems!
Basically, without getting to into it, the easy solution, besides tinkering with every possible "short wall set up possibility",is to put em in a larger space or set up on the Long wall. You'll likely have an easier time getting fuller more balanced bass if your seating possition is good.
I personally have yet to hear a set up for the IV's/V's where they sounded good too close together, or in smaller more confinded locations (such as along the "short wall".
If none of this is an option for you, your focus/target should be to do whatever you can to ensure all the woofers and boundaries are not at "multiples" of each other.
If I were you, I'd try the long wall set up as a comparison, and also seating location. At least then you can figure what the speakers can do in a potentially better set up scenario.
Don't dispare, the speakers have Bass. But also be aware that your set up is likely the problem..infact, I"m sure of it. I've heard those speakers have excellent bass in larger room layouts than yours. Infact, my buddy has the same problem in his "short wall/smaller room setting" as you with this SCIV's! His bas has sucked sinced day one with these. I told him it's his set up also...he's just too lazy to fix it.
