That thing came out a decade ago...makes sense they stopped supporting it a few years back. I'd imagine onboard sound is as good or better than that card...especially with boards you're looking at that use the alc1220 or latest alc4080 codecs (see specs of mobos to see which codes is used).
FTR you can put an x1 size into any of the larger slots. In other words, an x1 size fits and works in x16 (x4 and x8) slot(s).
...but again, I wouldn't use it...today's audio on the boards you're looking at (any... youve waffled on in this thread, lol) will be plenty good. I think you should pick something and go with it. It's not this complicated.