HDMI cables vs RCA/coax for sound in a HT system

I am debating between buying the OPPO bdp-103 and the -105. My question is: for the audio alone, are coax cables (RCA) better than HDMI--or doesn't it matter? I have Aragon 8008 and Aragon 8008x3 amps, Rotel processor, PSB Image speakers, and am making the move to blu-ray for the first time. I want to make sure I get the best possible audio in addition to great video. Will HDMI give me as great audio as coax cables if I play both Blu-ray Discs and cd/sacds? Or should I be planning to use HDMI for the video and RCA/coax for the audio? Haven't been able to discern a clear answer from other previous postings. Thanks!