Hi Mic,
"What I want to know is that I'll be getting a higher fidelity sound than Redbook by buying software in SACD."
Of course, you need a new player in order to play back an SACD. A single layer SACD will not play on a Redbook-only CDP (you probably already know this, but it wasn't clear from your question)
There are now dual-layer SACDs that have both a Redbook and an SACD version of the music on the disc. You CAN play a dual layer SACD on a Redbook only player, but you're listening to the Redbook version, not the SACD. However, there is a good chance that the new Redbook version encoded on the dual layer SACD will sound better than an old 80's or early 90's version of the same album as it will have been re-mastered in 2000+ with today's superior technology.
"So, obviously, for titles that record explicitly in DSD, they will be better than Redbook. "
Anything actually recorded in native DSD and played back on an SACDP will represent the best fidelity available on planet earth today (of course, the recording itself has to be good, but, "duh"!)
"What about "remastered" or titles that you know are more than a few years old? What exactly is involved in the "remastering" process anyway and how does that change the quality?
In the years since CD was first introduced, the equipment that transfers the analog master tape to digital format have improved dramatically. That's why newly remastered CDs (say '98 to present) sound so much better.
"Or, does it merely transfer the same recording, albeit at a lower fidelity, to a hi-fi format such as SACD? "
An analog tape transferred to SACD and played back on an SACDP will sound superior to the same analog recording transfererd to a Redbook CD and played back on a CDP.
"How will the sound on SACD compare to Redbook?"
Again, the SACD version of any recording, even if it's an old analog jazz tape made in the 50's (Miles, Billy Holiday, etc.) will sound better the Redbook version. SACD has higher resolution and contains more informantion than a CD.
Good questions!
markl