You are smart to look at improving your source and you should do this first, but $7K or more for a new transport?
The source is certainly important, but there is no need to spend this kind of money on a source. The ONLY thing that matters from a transport is the jitter at the end of the S/PDIF cable. Nothing else matters, nothing.
You can use your current transport if it still works well and reduce the jitter from your transport to ~20psec by inserting a Synchro-Mesh reclocker and a reference BNC cable from Empirical Audio. With the maximum performance upgrades of Dynamo power supply, Standard BNC input cable and Reference BNC output cable, the cost is $2172.00. You can get your toes wet with as little as $599. Here are some jitter plots of a typical transport and what the Synchro-Mesh can do:
http://www.audiocircle.com/index.php?topic=154408.0
Here are some customer feedbacks:
http://www.audiocircle.com/index.php?topic=154039.msg1651590#msg1651590
http://www.audiocircle.com/index.php?topic=154039.msg1655541#msg1655541
http://www.audiocircle.com/index.php?topic=154039.msg1661720#msg1661720
http://www.audiocircle.com/index.php?topic=154039.msg1658094#msg1658094
Even spending $10K on a new transport might not get you low jitter like this. If you want to improve your imaging, bass, dynamics and clarity, you must lower the jitter of your source. You can use this device with ANY stereo source over S/PDIF, using coax, BNC or Toslink, including Sonos, Servers, transports, iPod Docks, some Laptops, Smart TV etc.. If you do nothing else, replace your coax with the Reference BNC. 30-day money-back on everything listed, less shipping.
http://www.empiricalaudio.com/products/synchro-mesh
And don't sell that DAC yet. See what it can do with a low jitter source first.
Steve N.
Empirical Audio