Hello Kenyonbm,
It is your decision, of course. However, your logic seems to me strange a bit.
I bought SA-50 and have it for two weeks - extraordinary sound, particularly highs and midrange. Bass is a bit shy but is inmproving everyday so in 500 hours or so I will have better opinion.
Next, technical specs. Its S/PDIF inputs are of highest resolution matched only by $8K Cary Pro 306 (but I can't stand Cary sound and its personal) and next level is at $15k - a few SACD Players there.
Regarding USB you wrote:
"the 16/44 limitation on the USB input make the SA-50 unsuitable for exploring High Resolution audio"
Well, its depends on the definition of "High Resolution Audio" If its "24/96" then yes, you can find Ayre and Wavelengh DAC's which accept them ( but then why to ask about SACD Player if you are looking for DAC with very specific requirment).
"24/96" is not the HighEST Resolution Audio available to consumer, today. Reference Recording, Chesky, 2L etc produce 24/176 and 24/192 software and no USB today is capable to accept it (Ayre promised it by the end of this year - but we are not there yet). You could nicely use Weiss DAC-2 which accept firewire as a part of your music server and then send true hi-res info to your SACD Player capable of accepting it. If there is no money for DAC-2 then RME sound card and if too expensive as well then Lynx.
At any rate, good luck with your choice.
Rafael