Who's Shallenge?
Yes that's the card I use. You don't need it unless you are doing sound editing, generally speaking. The Z that you listed at the end of your post is a great card.
Yeah, the reason I am on the fence about your card is that some of those cards use software processing instead of a dedicated processor for 3D positioning. CMSS-3D can be either a physically present processor, or software. I have a X-Fi external DAC that does the same thing. What it offers though is the ability to plug it into a computer without having to do surgery, and then having right/left RCA inputs but lacks ASIO. ASIO is important for reducing lag. Sound Blaster makes some external DACs that also offer Core 3D processors, but they run $350-$500.
The difference in software and hardware 3D positioning is precisely what you have mentioned, which is inaccurate results. Another indication is lag in heavy traffic locations while playing AH2 (I haven't seen enough traffic in AH3 to know about it). The ZxR will not have that problem, nor will the Z. I have heard that the Zx has reduced quality, but I don't why it would.
The new Z, Zx, and ZxR use SBX, which is a marriage of an improved THX and CMSS-3D. For the money the Z is the best bang for buck, especially for games that use 3D positioning to the extent that AH does.
There is a huge difference between XP and the way every Windows release since has handled audio. Basically, the way I look at it the Extreme Gamer cards died when Vista came out. They're not junk, because they can still produce really nice audio. They just don't measure up to AH, especially in ground vehicles and now with Windows 10 I think they may be not very useful at all. It's impossible to be sure through rumors, and anecdotal experiences, so I haven't told you to bin them yet.