I must have read two posts back to back and responded to them in a single one so here's the relevant points for this one. Sorry.
A. CD5 vs CD5S
The major differences are:
1. USB input (48kHz vs 24/96kHz)
IMHO this is a moot point. The USB input is acceptable but not fantastic. If you can score a good deal on a preowned CD5, go for it. Save your moolah for a standalone USB-SPDIF or FireWire-SPDIF device and hook that up to the AES/coax input on the CD5. I have had great success with a Wavelink HS and a Weiss INT202
2. preamp stage
The CD5 I believe uses a digital volume control. The CD5S uses an analog preamp volume control that is only beaten by Ayon's dedicated preamp with built in regenerator. If you are using an integrated Triton or have a good preamp, the premium of the 5S is IMHO not worth paying for.
B. SACD vs RBCD titles
SACDs have enjoyed a resurgence of late. But you have to pay for it.
I have imported loads of SHM SACDs from Japan. Go to www.cdjapan.co.jp and have a browse. You'll be surprised at what titles you can find on the SACD format. Rolling Stones, The Who, Queen are all getting released on this format. Universal Japan is also re-releasing some old DVDA titles in SACD format. Of course, Pink Floyd's Wish You Were Here has just been released on SACD. So it's more than just jazz and classical.
If you are prepared to spend that kind of money, and also look around at Amazon Merchants to buy some Out Of Print titles, you would most likely run out of moolah before you run out of titles to buy ;)
Of course, you'll always have more RBCDs to choose from. But I do find that with the new remasters, there's extra care in the mastering/mixing that you get a big boost in quality. So you do get a better quality transfer with SACD.
C. Ayon CD5/5S vs SACD player
This is a bit harder to answer.
I will say this for the Ayon CD5S. It's a great CD player. Even with not so well mastered RBCDs (and there are plenty), the music still flows. You don't get ticked off with too much digital glare. And it does this without being overly warm. There's still enough detail and dynamics to keep me satisfied (and I was a SolidState guy through and through before the Ayon)
To get an SACD that can go better than the 5S, I had to go to something like a Playback Designs MPS5 or XDS1. And either cost a fair bit more than the 5S, I reckon. I'm not sure if you want to spend that much more.
I found the MPS5 I had on demo with the Audio Research Reference 5 had as much of the lush midrange and 3 dimensionality of the CD5S acting as a preamp directly.