Recommend upgrade DAC

Currently using Cambridge DAC Magic with SB Duet. Have no real complaints and could happily live with it. But, what would be a nice step up in a DAC for around $800-1000 used? Possibly with HDCD decoding?

Also, all CD's ripped to FLAC. Will ripped HDCD's be recognized by SB Duet and pass them on to DAC?
Wavelength Proton (uses USB to power the necessities)
Benchmark DAC1 (no USB for this model but they have DAC1 w/ USB with additional cost)
I don't need, or want a USB input. Squeezebox Duet connects to DAC using coax digital cable.
Is Benchmark DAC a major step up from the Cambridge DAC Magic? If so, please discribe.
I would think you are getting close to the most recent model Bel Canto DAC on the used market. I have a Bel Canto with the SB Duet and am happy using the coax.

I also have another SB Duet on the Cambridge DAC Magic and that seems pretty close. Finally I have a Musically Fidelity V-Dac on another SB Duet. That is a lower grade system but sounds pretty good too.

I think the SB Duet does need a DAC to make the sound into music.
Tough to beat the Cambridge DAC Magic on price to performance but I like the pedigree of Benchmark DAC1. Less of the off the shelf market components and a lot of in-house development of components and software.

You want to see some type of innovation like the UltraLock¬ô jitter-immune clock-isolation technology versus using general parts.
You can get this new for under $1K: