thank you for your attention and feedback. I am still hashing over the 9000 vs 999 debate. I have, though, found two opposing answers to my original question: Of the two, which is better for 2-channel audio?
Joel Brinkley, in the January 2003 edition of Ultiamate AV, had this to say in his review of the 999: "At the moment, I have two copies of only one SACD: Yo-Yo Ma's Solo (Sony Classical SS 64114), a superb 2-channel recording. I was able to perform a direct A/B comparison using my two copies played through different analog inputs of my Lexicon MC-12B processor. When I did this earlier this year, comparing the S9000ES with Sony's DVP-NS900V, I could detect no significant difference between the players. This time, comparing the S9000ES with the NS999ES, there were greater differences. The solo cello sounded a bit more open and clean, a little richer from the NS999ES. The difference was subtle, but it was there."
The link to that review is the following
On the other hand, Shane Buettner reports in his review of the 999 in the Feb/March 2003 issue of The Absolute Sound (Issue 140, pp. 57-59) that, "good as the  is though, it did not quite equal the performance of its predecessor, the Sony DVP-S9000ES, with virtually all two-channel audio formats: SACD, CDs, and 24/96 DADs. The DVP-S9000ES was more open and extended on top, had fuller bass that made the DVP-NS999ES sound a bit lean in comparison. The DVP-S9000ES was also slightly more transparent, with better resolution of low-level details and more soundstage depth" (p. 59).
I wonder if the 999 still had some breaking-in to do....?
So... I will probably go for the 9000, use it as is for a while, and possibly research the world of modifications at a later date. I might be happy with the 9000 as it is. I'm curious to hear how the 9000 combines with the Musical Fidelity X10-D in the signal chain to my preamp. The X10-D warmed up/filled out the sound of my cheapo players.
If I have anyhing of import to say, I'll get back on this chain.