I'm a little confused about your question and problem. The Meridian 568 has 4 digital coax inputs and 1 digital optical input, but these are provided for use with different digital sources. For dts, ac3, cd, and some 2-channel 96khz audio inputs to the meridian from your player, you only need 1 of the spdif (coax) lines. The Meridian processor is not set up to take 5 or 6 channels of dvd-audio digital input (meaning fully decoded mlp with 5 or 6 discrete digital output channels) because that requires both encryption and a 1394 or proprietary digital interface (such as that on the Meridian 800 series).
If you are looking for a dvd-audio player that provides 6 channels of digital output for dvd-a, the only current ones are the Meridian 800 and a player/processor that Pioneer is coming out with in the fall (DV47AI) - hope I haven't missed any others. Otherwise, you will need to settle for analog outputs with dvd-audio, until more equipment comes out with the 1394 interface.
If you are looking for a dvd-audio player that provides 6 channels of digital output for dvd-a, the only current ones are the Meridian 800 and a player/processor that Pioneer is coming out with in the fall (DV47AI) - hope I haven't missed any others. Otherwise, you will need to settle for analog outputs with dvd-audio, until more equipment comes out with the 1394 interface.