Anthem CD-1 tube upgrade?

I recently got an Anthem CD-1 for use in my office, and I love the sound of this thing. Don;'t know whether it's the tubes, but it just sounds sweet. This has the factory tube in it. Is there a simple, drop-in replacement that wo9uld make this player sound even better?

(Sorry, I dnot even know what model the factory tube is, if that tells you anything :). The rest of the system consists of of a Headroom Max amp and Sennheiser HD-600 headphones. I listen to just about every kind of music, from Classical to Techno.