Even though I love SACD and was the one who turned Peter on to it, if I were in your position I would go for the Von Schweikerts stereo setup. I think a convincing stereo presentation is a lot easier to pull off, whereas a convincing multichannel presentation is much, much more difficult. With a few exceptions, most multichannel SACDs I've heard use surround channels for exaggerated effect rather than increasing realism, pleasing though it may be (though the exceptions do sound quite impressive). Plus the selection is rather limited and who knows how long it will take before it really catches on, if at all. Who knows, maybe by the time it does you'll have another 'windfall' that will allow the addition of more Von Schweikerts!
On the plus side for SACD, you could get an SACD player now and still keep a stereo-only setup - all SACDS have a stereo layer (many are stereo only), so you could enjoy the benefits of DSD now and decide later if you'd like to create a full multichannel setup.
I say go with stereo. You've already got multichannel in your HT, and with the opportunity you have to really dedicate a room and fine tune a setup, I'm sure you could create something really special.
