Which Would You Choose?

Neither. I would take the JC 5 over either one. Not sure why you think either of these would be an improvement. 

I auditioned the S5 against a Luxman M10x. The Luxman was clearly better, as it should be for $20K. However, the Michi was very impressive for its price. It's definitely a great value in this crazy, high-end world. However, depending on your listening preferences, don't rule out a McIntosh MC462. The S5 is slightly more detailed, but the McIntosh presents as warmer and more real with a tremendous bottom end. 

What specific improvements are you looking for over the JC5?  Also, I’d consider upgrading the Monster 3600 that can’t be doing you any favors sonically.

@soix 

+1

Naturally, upgrades in components should yield improvements in sound. This is a complex subject. I could go on forever. Before you go that route, I would suggest improvements in all of your cabling. There are currently several high-tech sources that have "finally" discovered the sonic benefits of using 7n's OCC solid core copper wire, with silver plating, as the main ingredient in all of the cables offered, Including highly shielded power cord construction. Personally, I use custom made cables utilizing this material and construction, however I have recently come across a manufactured source that I would buy in a heartbeat if I didn't already have what I have. I suggest contacting DECAWARE in E.PEORIA, IL. Talk to STEVE DECERT about all of his current OCC cable designs. This person is truly an audio design genius, so you can ask him anything. BE CAREFUL though !! "All of his component designs are incredibly addicting, including speakers. His company is one of those hidden gems in the HIGH END audio business.