The Montego DDL is capable of receiving/sending 24-bit/96kHz audio streams 
at both its S/PDIF Digital Input and S/PDIF Digital Output. 
The Catalina was limited to a maximum of 16-bit audio at its S/PDIF Input. 

96kHz sample-rate Analog Output: 
  The Montego DDL can play back 24-bit/96kHz audio through its analog outputs.
  The Catalina was limited to a maximum sampling rate of 48kHz through its
  analog outputs. 

Environmental Effects: 
  The Montego DDL provides a wide selection of soundfield-enhancing DSP 
  effects. The Catalina did not include this feature. 

Here is a list of other DSP effects and features available in the Montego DDL
that are not available in the Catalina: 

- EQ with Presets
- A3D 1.0 support
- EAX 2.0 support
- Voice Morph
- Voice Cancellation
- Pitch Shift
- Interface for Windows Media Center
- Full-duplex D/A transfer

For more information on the Turtle Beach Montego DDL:
http://turtlebeach.com/site/products/soundcards/mtgoddl/producthome.asp
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