Hmm, I thought I'd read it in the manual. But looking again, it's not totally explicit is it?
Every reference to SACD has a footnote saying "VSX-AX4ASi only" (I'm looking at the UK manual here - that's the 84TXSi). And that's the only one with the i.Link, suggesting that the i.Link is required for SACD. But it's not conclusive.
There is one more suggestive reference though - the "SACD Gain" option. The footnote for the SACD Gain option finishes with
(VSX-AX2AS only - The feature is intended for use with future improvements to the HDMI interface)
This suggests it is just that the HDMI interface currently doesn't support DSD transfer, rendering the option pointless for the AX2AS/82TXS.
I wonder if they're really intending an upgrade? Probably not - they just couldn't be bothered having a different UI for the two models. But it's conceivable that lack of DSD over HDMI is just a firmware issue; maybe they've fitted a capable chip and wired it up, but haven't put handling code in place due to not feeling able to test it at this stage, what with the lack of players.
(As an aside, the SACD Gain option is an example of one of the processing difficulties in DSD->PCM conversion. PCM clips at 0dBFS; DSD allows excursions up to +3dB, and maybe even +6dB. The 3dB limit is enforced by the tools and the pressing plant, the +6dB is the theoretical limit of the format. When converting from DSD to PCM you'll probably have to lower the level by 3dB to avoid clipping. The Pioneer seems to default to a 6dB drop, but lets you raise it back up.)