Budget DAC with Optical Digital input

Putting together a portable system for some travelling I'll be doing this summer. I am getting a Sony Discman with an optical digital out, some Senn 600's, a headphone amp (undetermined, tubed would be nice). Something with at least a 20bit DAC chip would be nice, and the optical input is necessary. Detachable power cord is also necessary. Under $300 would be nice, under $200 would be perfect. If you have any suggestions or alternatives to my proposed setup please let me know, Eric
I have a Monarchy 22A which I picked up for $230 used here on Agon. It was a significant improvement over my Marantz CD67SE, and a HUGE improvement when I added a Monarchy DIP (which cost me $95, again on Agon). The Marantz is not a high end player but it's certainly a good player.

The 22A has optical or coax inputs, 20 bit burr brown DACs. If you use the DIP it will translate optical to coax (SPDIF) so you can use a 75ohm digital cable to the DAC. Oh, and both have detachable power cords and are built like tanks .. great for travelling.

I did not compare to the MSB link DAC which may be another contender.
Assemblage 1.0 DACs have optical out and should be had for around $150 used. Very good and overlooked piece.
Channel islands Audio VDA-1, $349, optical in, small too:

Cal Audio Gamma
If you can find a Micromega Microdac for around $200 or so, I would recommend listening to it. I have compared this to Rega Planet, MSB Link I and Art DI/O and it beat them all. Not the most detailed dac around and a little light in the bass, but you won't find anything smoother at anywhere near this price. If you're gonna use a portable cd player as a transport, suggest you get a used jitter reduction device. The Microdac does have both toslink and coax inputs and removeable cord.
If you need smooth,GDA-600 from Adcom might be the ticket. The GDA-600 came out in 1994 (I believe) and was Stereophile Class C. It has input for S/PDIF over RCA/coax and toslink plastic. It has has an aes/ebu input, if that matters. Smooth sounding, and not bad since you can find these for $200 used on the street.

You might see a GDA-700, but all it really adds over the 600 AFAIK, is HDCD. Both units can handle 20bit/44.1k. It also has a detactable IEC. Unfortunately the unit is quite large (footprint). So I doubt it is very portable, if that is part of your requirements.

FWIW, I used a GDA-600 until I switched it for an EVS Millennium DAC I.