Hi,
I'm using Marantz Sr5600 for several years now and it just works flawlessly. Great decision, never regreted - it's controlled over rs232 (in my case as two independent outputs - two zones configuration).
In my living room there is some non rs232 amplifier hooked up to MD and TV and USB UIRT and I after 1 year I still haven't set it up properly. I'll probably purchase another rs232 controlled receiver sooner than do proper setup for it... :-)
Regards,
Bulek.