AR CD3, CD5, or CD7?

I can't comment about the choice of ARC CD Models, but I can say that staying with ARC componets throughout the system will likely insure that the nasty hums and buzzes that plague many system will be minimized. I also feel that leading edge companies like ARC design their gear with certain sonic attributes in mind which may never be realized with a 'hodge-podge' of different componets.

As Eee3 stated, it all depends on your budget. I now use the CD7 and previously owned the CD3mkII. To me, and speaking only for its use in my system, there is a noticeable improvement across the board. Better tonality, clarity, rhythm, pace, dynamics, micro-detail, noise floor, etc. How much better, and how much that difference is worth, only you can decide. The CD3mkII is a great player, and for the money, is very tough to beat. With your system, I believe either player would provide great synergy.

By the way, your LS17 preamp is a real sleeper--definitely underrated and a great piece of gear. Happy listening.

If you can afford the CD-7, that's the way I suggest you go. I have one in my system and like it very much.