I have very little experience with McIntosh, but I've always liked the way they sound.
Given that the McIntosh 4100 is from about 25 years ago I'd venture that the Onkyo is faster and more articulate. It also has more power (at least on paper) into a 4-ohm load. That doesn't say which one you'd enjoy more. If you pay fair market value or less for a Mac, you'll usually get your money back (or more) when you sell it later.
Given that the McIntosh 4100 is from about 25 years ago I'd venture that the Onkyo is faster and more articulate. It also has more power (at least on paper) into a 4-ohm load. That doesn't say which one you'd enjoy more. If you pay fair market value or less for a Mac, you'll usually get your money back (or more) when you sell it later.