Well,
I didn't have the good fortune of listening to both - but I do own a C-28 and a Marantz preamp. However, the Marantz is an Esotec SC-6, so it might be a bit fancier than the 3600.
I have the Esotec in my main system, as it sounded better than my C-28 with my than setup. However, Once I moved the C-28 to the home office system, it sounded better than it did in the main system - guess its a synergy thing.
I personally think they are suited for different types of music: the C-28 has a fuller sound and is better suited for Jazz, Blues and classic, while the Esotec is better suited to rock and pop.
I personally would have listened to both if possible.