X-Fi isnt supported by KX - so if you want to use KX... X-FI wont work.
But Ill point out the differences between 10K1 and 10K2 chips... or at least I can tell you the differences between my SBLive value and A2ZS. Maybe someone with an Audigy Plat Ex can give more description about the differences.
10K2 has more DSP resources than 10K1 - More GPRs (512 instead of 256), More XTRAM possible, More iTram (192 instead of 128) More Instructions per sample (1024 instead of 512) - all thise equates to how many KX DSP plugins can be used at any 1 time.
So, just from DSP resources standpoint - may help you to decide
Then theres the IO box a platinum usually comes with - Which can be very handy - for me adding additional Ins and Out ports (Mine made use of every IO described on the AUD_EXT pinouts) - but I think the eX doesnt have this connector - and Im not sure what IO it has - but I bet the codecs are better than the ones used in the Live cards.
So if its a good price - and you verified that the card works AND verify is supported by KX (Im pretty sure it is, but??)- It just seems like you have more to gain - if its worth the money, thats up to you.
X-Fi - for the price dont seem worth the ammount money they ask. Maybe when X-Fi V2 come out and they 'DUMP' the V1's at half the price (seems to be the pattern) - but I can NEVER justify buying the 'latest and greatest' of anything for a PC - the 'Bang for the Buck' is just TOO low - for the budget conscience like me, as I assume you are also - otherwise you would be in here wondering 'when KX will support the X-FI Elite Pro'.
Hope that helps...