I had both a Marantz AV550 and a Marantz SR880 receiver along with a Marantz CC65 Cd player. Let's just say I miss the 550 but not the 880 nor the cc65. This is why: Marantz features are great and easy to use. Marantz amplification is only mediocre sounding (flat)in comparison to other amps that are just a little more money (newer adcom, nad, sony es, rotel...). I honestly think you will be quite dissapointed with the older NAD amp. Also, marantz single bit cd players work great but don't sound nearly as good as similar cds from denon and rotel.
My suggestion: Keep the 550 for now, spend your money on some very nice amplification and see how that goes. The 550 with a nice adcom or rotel amp should blow away the NAD. You've got beautiful sounding speakers, let them sing!
My suggestion: Keep the 550 for now, spend your money on some very nice amplification and see how that goes. The 550 with a nice adcom or rotel amp should blow away the NAD. You've got beautiful sounding speakers, let them sing!