Until you upgrade your sources to lower the jitter, the differences will be small. I continue to hear audiophiles say that a $200 DAC sounds the same as a $2000 DAC, or that all DACs sound the same. This is why I highly recommend upgrading your source or reducing the jitter from it.
Here is typical jitter from a transport:
http://www.audiocircle.com/index.php?topic=154408.0
If you intend to use a transport, then you have 2 choices: buy a very expensive transport to lower the jitter ($5K+), or use your current transport and lower it's jitter with a reclocker like the Synchro-Mesh ($599).
Once you have a low jitter source, only then can you properly audition DACs and S/PDIF coax cables. Then you will hear the real differences and be able to make an informed choice.
Unfortunately, you will not be able to do SACD with an external DAC. You will still need the analog outputs from your CDP. Nothing much can be done about SACD jitter, except to mod your DAC, which will reduce jitter, but not nearly to the level of a good reclocker. If you don't have a large SACD collection, don't bother. Your CD collection will probably sound better than the SACDs anyway. Treating CDs with coatings and other tweaks to reduce CD jitter are not necessary if you use a Synchro-Mesh reclocker.
Steve N.
Empirical Audio