Optical Toslink vs.. RCA SP/DF cables best??

Hi. I recently introduced my old Denon DCD-3910 universal/DVD player to my dedicated 2-channel listening room to take advantage of its DVD-A and SACD playback capabilities. The Denon actually has 3 pretty good 24-bit Burr Brown audio DACs per channel internally, but I thought I'd use the digital inputs to my Cambridge Audio Azur 740C vII 96/384 hi rez CD player/DAC as an external DAC for the DVD-Audio digital signal. After extensive fiddling with the Denon's on-screen programming, I have the Denon set up for high-rez 2-channel audio analog & digital playback only. Thus I have the SACD signal converted by the Denon's internal DACs and output through the analog outs and directly into my Musical Fidelity preamp, and the DVD-Audio digital signal output through the Denon's digital outs through an optical cable into the Cambridge's optical digital input. The sound is very good, and it is interesting to compare the DVD-A signal through the Cambridge's external DACs vs. the analog SACD 2-channel signal through the Denon's internal DACs. Two important questions: Is the Toslink optical cable or the RCA cable best for a 1 meter trip from the Denon to the Cambridge? Second, some have told me that 2-channel high-rez DVD-A signals cannot be transitted through Toslink or RCA connections, but only through HDMI or I-Link connections. The Denon is clearly doing it. What gives? Thanks!
The rest of my system consists of:

Musical Fidelity A3cr dual-mono amplifier
Musical Fidelity A3cr dual-mono preamp
Perreaux MC phono preamp
Vintage Denon DP-47f turntable
Ortofon Samba low-output MC cartridge
Cambridge Audio Azur 740C vII CD player
TrippLite 2400 power conditioner/voltage regulator
Von Schweikert VR-4 loudspeakers
RBH external subwoofer amp
RBH VPS-12 passive sub
all high-quality interconnects