Thanks again for the info. Well, the connections to the power strip are pretty snug. The two-prong male connectors (C18) at the other end of the power cables (that came with the amps) are not the most reassuring, as they have some slack. I have tried to push them in a bit, just in case, but that's as far as they get. I think that as long as they make contact, they should work fine.
The xlr connectors are all the way in. I pushed them in until I heard them click, so these are fine too.
Yesterday I came across an interesting thread by a guy who claimed that the buzzing sound is normal in separates that have not been grounded properly (http://forums.audioholics.com/forums/amps-pre-pros-receivers/70111-marantz-av7005-networking-v-processor-review-13.html
He used some wires to connect the chassis of the prepro with that of the power amp and then to a ground. He says that in general it is unlikely that both prepro and amp are at the same potential, so there will always be phantom power that needs to be driven to the ground. I am not sure I want to start wiring the back of my system to cure such a faint buzz (can only hear it a few inches from the mid-frequency driver). If it is just that and not a faulty prepro, I can go to sleep at night knowing that.
I've just finished testing the buzz with the method you suggested. I connected the analog outs of my old Sony DG820 receiver to the unbalanced ins of MM8077, connected the ins of the Sony receiver to my blu-ray player's analog outs, flipped the switch from balanced to unbalanced on the MM8077 and … I still got a buzz through the speakers!
So, it seems that it is a grounding issue. Well, …
I thought I'd let you know, after a few days of monitoring, that the high-frequency static noise from the tweeter is of a transient nature. E.g. I noticed today that I could pick it up more on the left surround! Very weird. It seems to be some sort of RFI. Again, it is mostly very faint. I only noticed it the other day when it suddenly became audible from about 3 feet away, as it sounded like stepped intermittent hiss: _____
Finally, I would like to ask you about the tripp-lite power strip. Before getting the Marantz equipment, I researched to death whether I needed a fancy, line-filtering power strip. I decided that I didn't need one, as many people say that unless you go for a proper solution, like PS Audio, you are not improving anything. Of course, I would not want to spend that much on power regulation. The cheaper solutions of a filtered power-strip sounded appealing but people either say that it affects the soundstage (weird) or that it makes no difference. Especially with products like the Monster HTS 1000, people have reported lots of problems, incl. buzzing, malfunctioning, etc. Perhaps this Tripp-Lite product is adequate and it doesn't cost very much. (I was once very close to buying the Oehlbach Powersocket 608, http://www.oehlbach.com/en/home-cinema/power-home-cinema/powersocket-908
, but I chickened due to the price and that it may not make a difference, after all.)
Thanks for your suggestions.