2 of the 8 analogue outputs on my fireface 800 do not produce signal - and one clips.

Within Pro Tools, I routed 6 tracks containing signal generators, to 6 of the 8 analog outputs on the Fireface 800. Channels 7 and 8 failed to produce a signal, and channel four produces a sustained clipped signal. This is also the case when looking at the fireface mixer software. I have attached screenshots outlining the test I ran. I have not included I/O for channels 1 and 2, because I know they work - and use them as my main outs. I also used the same cable for each of these tests, and even tried several different ones once the problem had been established.

Why would this be? Have I missed a key feature? Or does it look like there is a problem?

[img align=c]http://i368.photobucket.com/albums/oo130/creativecorps/Screenshot2012-02-25at015429.png[/img]

[img align=c]http://i368.photobucket.com/albums/oo130/creativecorps/Screenshot2012-02-25at014308.png[/img]