Reviews will have bias in the same way that I described, even at lower price points. Even if the audio was to sound identical, it is possible people would nonetheless highly rate the device.
Given that, we can look further into the Audigy FX. No insult to Geek-9pm of course but I would expect that it was a rather quick look around with assumptions of manufacturer goodwill; as it happens, though, Sound Card Manufacturers can be pretty shady.
For example, in this case, "Audigy FX" would suggest that it uses their Audigy Audio Chip. The Audigy Chip is a fairly capable audio processor, quite powerful and capable especially for WinXP and Windows 98, which benefit much better from the hardware capabilities of the card.
However- As it happens- The Audigy FX doesn't have an Audigy Processor at all- it uses a RealTek ALC898 Chip. This is a common audio codec chip used in many Motherboards. For example- the motherboard I'm using has the exact same chip (GA-Z87X-UD3H). Most of the value in the card comes from the software, which provides effects that are provided via hardware on their other cards, but which instead perform processing on the CPU.
While I've not had an Audigy FX, I did have it's predecessor, the Audigy SE. This used a similar chip generally used for motherboard integration of audio, but placed on an expansion card. While it certainly sounded fine, it made a lot of software unusable, because all of it's audio processing was done in the driver via the system CPU, and not on-board the audio card. This made even relatively simple games like Doom Source ports completely unplayable (4 FPS), as all the audio processing was being done by the CPU- even replacing it with a generic PCI Sound Blaster 16 showed a marked improvement.
Given that, one alternative may be the aforementioned ASUS Xonar DG. You can find this as a PCI or PCI-E model. And, while it does use an Audio chip that is found on motherboards, It is only higher-end "Audio-oriented" ASUS Motherboards which feature it- whereas the ALC898 is all over the place.
Windows 98 and XP are particularly well served by appropriate era-accurate audio hardware. Particularly through games certain Hardware capabilities can be utilized, many of these were dropped on later cards due to changes to how Windows dealt with Audio- EAX, Aureal3D, Hardware-accelerated positional Audio, etc.
