You actually asked a few questions all jumbled into one. So here's my attempt to make some sense of it all.
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.
You mentioned you heard the CD7 before this. I suspect it's the CD-07S) and was impressed. I had a pre-owned CD2S (two models up from the 07) for about a week and it was so good that I was convinced to top up the difference to get a new CD5S and did not regret it one bit. The improvement even between the 2S and the 5S was not small.
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.
DAC vs CDP/DAC
I have taken steps to rip my CD catalog in AIFF format. It's a tedious process, and with about 70% done, I think I have a large enough size to be usable since most of my frequently played titles are there. I love the convenience and for background listening, it's pretty damn close with my custom SSD Mac Mini/8GB/SSD/Pure Music setup, Wavelink HS to the Ayon. But if I listen intently, I'd still say the spun disc has just that more "life" and "energy" to it. It's close, and I expect in a few more generations, we might just supersede it. But in the meantime, I enjoy the best of both worlds: putting on a disc when the mood takes me, or using my music server to serve up a playlist of the moment.
I know I haven't given you an indication one way or the other :)
ps Melbguy1, glad to see you online again :D