In addition to those you're considering, I would consider the Denon 3910 or a Sony XA555ES.
The Denon players give you the option to play DVD-A, HDCD, SACD, and pretty much anything else. You can find the Denon 3910 for $250 or less all day, and there are usually 2-3 of the modified 3910's here for $5-600 (some like the APL 3910 go for much more). The 3910 was a $1500 player that plummeted in price because of blu-ray, but for audio it's still very good, and can be modified to be excellent. The stock unit would definitely save you some money and I believe is as good or better than everything in the sub-$500 price range.
The Sony sounds great as well, and gives you the flexibility to load up 5 discs at once. It's less flexible as far as format is concerned (CD/SACD), but those are going to be the go-to audiophile formats for the most part.
The Marantz and Emotiva suggestions from Rar1 are good as well. Definitely keep your options open.
One last thing to consider, especially if you're only looking for CD playback, you may find the best bet is to just buy a Sony Playstation. The PS1 (SCPH-1001) is a great and very musical CD player, and an unmodified unit shouldn't ever cost you more than $50 (there are several on eBay right now for <$30 with replacement consoles at $20). It may match with your NAD 325 better than a NAD CD player. They're really musical machines, and you could set aside an extra $400 toward your next upgrade.
Good luck
