Have the opportunity to get a new Nad C545BEE or a used Marantz SA7001 KI, at a slightly higher cost, to replace my existing Nad C521BEE. Which would be the best option? Rest of system is Marantz SR5600 multichannel amp, Rotel RB980BX power amp driving a pair of MA S6's. Would either of these be an improvement over my existing player?