Conrad Johnson DA2b... "Is it the Tubes?

Yes my curiosity surrounds the Conrad Johnson Da2b. But first I must back up and explain my situation. I am looking for advise and feedback. The system I have now is the best components that I could afford to buy second hand. (being that I am only a 22 year old college senior). First let me explain my current system. Mcintosh 7100 amp, Mcintosh C-36 preamp, Pioneer Elite PD-65( as a transport), Conrad Johnson Da2b DAC(XLO digital cable connecting the two), B&W 602 II's, The interconnects and Speaker Bi-wiring were the Best Monster cable I could afford. Before the addition of the CJ and Elite, I was using a crappy sony 200 disc changer that had to go! When I made the upgrade I was not that impressed. My question is ...is it the tubes? The DA2b was 2 years old when I got it and still has the stock tubes. If so what tubes should I get? The new set up has added warmth to my music but it seems that much clarity is missing and there is actually less of a sound stage.I listen to everything from Jazz to classic rock. Being not that experienced in the audiophile world I may be wrong and it may not be the tubes at all and something else, but I know for 2000$ retail the DA2b should sound better than a sony changer and it barely does. HELP!! ps- affordable!! solutions will be greatly acccepted as well as critiques of my system as a whole! Thanks! Adam