75 ohm coaxial should be fine, I m using belden 89259 75ohm coaxial for my sacd with great results, 75 ohm coaxial would even work for digital coaxial cable if you want.
If you use one coax SP/DIF cable (I'm assuming that's what you're doing, if I read your question correctly), all you'll be outputting is a digital signal (DD/DTS) which some DVD-As output. If you want the "advanced resolution" on DVD-A Discs, you'll need 6 analog Interconnect Cables for your 5.1 outputs. Ditto for SACD.
My post was not clear: what I meant to ask was whether one can use six coax cables for DVD Audio or whether on should buy six dedicated analogue cables.