Originally Posted by Il Mostro
Look for older DAC's with the now-gone Ultra Analog 20 bit chips. Enlightened Audio Designs DSP-9000, Resolution Audio Quantum and others. While lacking the ultimate detail of the best current DAC's, it just does not get any smoother than this. You can get the once- expensive gear at great deals today and they still more than hold their own.
I'll second II Mostro's suggestion here, the older DACs are a steal and you cannot beat them for their smooth and 3D presentation, my favorite of the older DACs is probably a Meridian 563. However, the cambridge is pretty warm and smooth already. If you wanted to try something that might be a tad smoother, and modern, try a Jolida FX tube DAC, it also has capacitor output stage so you can swap those out to really smooth the sound out. Throw some Jupiters in there or something. Pick up a Theta DSP Pro basic, that will also be very very smooth and will blow the doors off most modern DACs anyway should only run you around 300.