For practical purposes and for most users, I expect they can be treated as equivalent. However...
The DCM475 has two tuners, allowing it to tune to two blocks of 4 channels each, where The DCM476 has only one tuner so all 8 channels must be in one block. That is, on a 475 you can tune to 95-98 and 84-87 to get your 8 channel bonding (channel numbers picked more or less at random). A 476 can only tune to one of those blocks. Presumably still allowing you 4 channel bonding.
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