I would think that the build quality on the Acurus is much better than the Marantz. The Marantz is a mosfet amp, while the Acurus is bipolar. In a general sense, bipolar amplifers are thought to be of a higher quality, as virtually all truly high-end amplifiers are bipolar in nature, and not mosfet. Again, there are exceptions, but I would lean towards the Acurus. This is coming from someone who has owned an Acurus A150 as well as Marantz MA500's.
