New to Music Fidelity A308 A couple of questions

"...Can I bi-wire and use all 4 posts (2 red 2 black) for each channel..."

Yes, you can. 

"...I plugged the DAC into the CD input I got a low level hum straight away..."

No idea on this one, they should be the same. 

As far as I can tell, the connection should be CD output into DAC input ... then DAC output into preamp input. 

My two cents: congratulations on on acquiring one of the best values in an older amp.
I’ve got one and I love its synergy with ATC speakers.
I agree with the last poster in reference to your questions.

Thank you. The sound quality is night and day compared to the Arcam A85/P85 combo. I could just not get the same umph out of those Arcam amps so I am happy with it. I did bi-wire the speakers - thank you and that all works well.

The last culprit is the hum noise on the CD input. 
- It does not happen when I plug in the same source into one of the other AV inputs
- It happens regardless what I plug into the CD input
- I tried plugging in the amp into another wall plug/extension but same results (it could also be that they are on the same circuit)

Any ides?

Thanks

Perhaps a ground loop hum.

Beats me. Do you actually need that input? If it were me, I would just accept that I have an amp with one bum input. Of course, I’m a little lazy around problem-solving with these things unless I need to.