If you are looking for something to enhance or change the tone I think there is a lot of options to choose from.
The apogee is a brilliant piece, but as far as the converters go they are some of the best as far as I know. So I doubt you can go too wrong with just using that.
If you are looking for the elusive analogue mojo then it might be worth having a look and listen to this
http://www.vintageking.com/site/files/heargear.html
You can listen to different preamps to get an idea of how they colour the sound.