I own the amp you are looking at. I also have 4 1/2" of top clearance for it my open rack. Absolutely no problems whatsoever.
As is the case with just about anyone offering a product or service, they are being overly cautious in this hyper-litigious society of ours. I believe their 8" caveat is right next to the warning not to spill any McDees hot coffee on it either.
BTW, its a great amp and I highly recommend it. I don't know what you intend on driving with it, but I drive a pair of 4 Ohm Vienna Acoustic Bach Grands with mine, and the Marantz has taken these speakers to new heights.
As is the case with just about anyone offering a product or service, they are being overly cautious in this hyper-litigious society of ours. I believe their 8" caveat is right next to the warning not to spill any McDees hot coffee on it either.
BTW, its a great amp and I highly recommend it. I don't know what you intend on driving with it, but I drive a pair of 4 Ohm Vienna Acoustic Bach Grands with mine, and the Marantz has taken these speakers to new heights.