Aged Adcom Conundrum/Question

At present, all of my listening is done via headphones (Sennheiser HD 580, Creek OBH-11 and Adcom GCD-700). To my my ears the sound is excellent, being free from excessive grain and harshness, yet possessing clarity and detail. I've seen Adcom GDA-600's for sale recently for prices below $200.00. Would it be an example superfluous redundancy to add the GDA-600 to the GCD-700? Logic and reason say no to me. But foresight and praticality say yes. The aged GCD-700 is at the end of it's expected lifespan. With the GDA-600 on call, a cheap player/transport can be purchased with the promise of quality sound due to the presence of the GDA-600. Though obviously having no mechanical moving parts, the GCD-600 is just as old. Should I consider a Beresford, Zero DAC, etc? What would be your advice?