Outboard Processor Question?

I have tried a number of different transports and dacs and currently run two systems with digital separates.
Firstly, I have found that a jitter reduction device such as the Audio Alchemy DTI Pro will improve the sound of most transports. I also disagree with the comment above about transports not making much of a difference in sound quality.
For a toslink cable, I would recommend the Monster Lightspeed 100. Some say the 2 meter sounds better than the 1 meter, but I have not tried that. I have tried the Lightspeed 200 and the lower priced 100 is better.
For dacs, I would avoid the Cal Gamma. I have read a lot of good things about the Sigma and have just bought one, but have not received it. Dacs to consider if you want something small would be the Bel Canto or Micromega (Duo BS or Microdac). Micromega's can be bought used fairly cheap.
I have not tried a Sony ES changer as a transport, but I know of one high end dealer that used to recommend them for customers buying high priced dacs that insisted on a changer as a transport. I use a Stan Warren modified Aiwa changer as a transport and it is a good transport, but not as good as a Parasound single play belt drive transport that I also use. If I had not stumbled across the Aiwa, I would have gotten a Sony ES to try.
I have not tried a lot of changers.

I just received my Sigma today and plugged it in. Right out of the box I can say I really like it and would recommend it over the Micromega and as a better value than a Bel Canto. These are initial impressions and should be viewed as such. But for around $300 or maybe less for a used one, you can't go wrong trying one. The Sigma has some of the magic of tubes and images better than the Micromega.

I can not A/B the Bel Canto against the Sigma. I owned the earlier version of the Bel Canto (just before the 1.1) for about a year. The Bel Canto had more subtle detail and a larger soundstage than the Micromega Duo BS2. The Micromega was a little smoother and richer sounding. The Bel Canto worked great for me while I was using it with a Parasound CBT2000 transport. However, for reasons irrelevant here, I needed to switch to a cd changer and that combination with the Bel Canto did not work as well. I was willing to trade some detail for tonal balance so I sold the Bel Canto. The Cal Sigma is a little more refined than the Micromega, but it does also present more information. I especially liked what the Sigma does with violins, which is one of the weaknesses of digital reproduction. Images seem larger, something I had not experienced since I sold my Theta processor years ago. Does it present more information than the Bel Canto? Tough call, but I can tell you absolutely that the Bel Canto is not 100% better which is about what the difference in cost will be (if not more). Consider this: if you buy the cheaper Sigma you would have $ left over for better cables, maybe some more cd's and you can play with tube rolling.

I am sure you'll find people who will give you various technical reasons why a dvd player makes a good transport, especially using the toslink output. Bel Canto recommends dvd players with their dacs. When I first got my Bel Canto I corresponded with two people who tried dvd players as transports only to find they preferred the sound of their cd players as transports. Since I liked what I heard with the transports I had, I never tried a dvd player as a transport.

One follow up point to my comments on the Cal Audio Sigma. I purchased an Ensemble Digiflux cable with it and this is apparently a synergistic match and partly responsible for the smooth sound I hear.