Spoogemonkey,
To follow up, I suggest you set a budget for your DAC, and then choose two or three used components currently selling at that price, plus two or three current/new DACs at the same price. For example, if your budget is $500, then look for used DACs currently selling around $500 regardless of their original retail price. Audition and compare them in your system with new DACs selling for up to $500.
For new components you need to work with local dealers who will let you borrow demos. Use forums and trusted reviews to narrow down your choices.
For used, as long as you don't over-pay and don't keep too long, you should be able to purchase and re-sell without losing any/much money. For used, again I suggest to keep it to not more than five years old.
As for Bryston, Ressonessence or any other brand, new or used really depends on your budget. I mentioned specific brands because I and/or others I trust, have generally positive experiences with. If new ones fit within your budget, consider them. If only the used ones fit, then consider those instead. Oppo as others here have mentioned also do well at their price point.