Preamp to pair with an Adcom GFA-555 mkII

Hi, I have an Adcom GFA-555 mkII amp, and a pair of NHT Super Ones. I'd like to hear opinions on what type of preamp would pair well with them. I love clear detailed vocals with little coloration, and a wide soundstage. I listen to a mix of music, rock, r&b, jazz, classical. Any ideas? I'm also open to ideas on speakers. Oh, preamp budget is <$500; speakers <$300 (also need to be on the bookshelf or mini-monitor size). Thanks!