used DAC for under $350 Channel Isalnd....

For the newest ideas in minimalist, over-achieving DAC's in your price range, take a look at scott-nixon.com where the assembled and shipped package price is $250 for the basic DacKit. If your budget is a little higher, then there are a few companion DAC models, also. For the special quality of tube output, there is the TubeDac where the assembled and shipped package price is $350. For new models from an esteemed designer-manufacturer, this is about as cost effective as it ever gets.
The industrial design statement of these miniature DAC's is reminiscent of my Earmax headphone amp, another miniature over-achiever, which fails to share Scott's bargain pricing policy.

Correction: the assembled TubeDac from Scott Nixon is shipped to a buyer for $400, slightly above your requested limit of $350. And the assembled DacKit is shipped to the buyer for $250, leaving you with some extra cash to buy more CD's.

Here on Audiogon, Viggen already owns the DacKit, and I think he has compared it to another new design with a higher bargain price. Perhaps he will comment on his unit which falls easily under your $350 budget limit.