I'm busing doing a home Demo with the new Nad D1050, I have an Arcam A18 and Nad C516. You need to really listen carefully to hear the differences in my opinion, it's not like speakers were you can hear the difference immediately in my opinion. I've managed to level match the dac with the CD player and the differences for me are small when compared to using the CD player without the Dac, but much bigger when using it through my media player. It's added more transparency when used with my CD player and I'm hearing more decay to symbols and more tonal character to bass lines, but they are small improvements, I've been AB testing since Thursdsy night and it's taken me a little while to start really hearing those differences, the biggest change is in the volume, the Nad Dac is about 4db louder than my CD player and a lot louder than my media player.
i reckon you need a really good system to hear what a dac can really do, using it for a Pc or Media Player will reap you the most benefits but trying to improve on modern CD players I think you will need an expensive dac and Amp with decent speakers to get the most out of it.