As my wife heard, the deep bass was a tiny better with the TOSLINK cable than the RCA so I was at an impasse. However, I had planned to make another modification to the woofer's crossover network in my speakers and now seemed like a good time to do so. With a 4-ohm woofer, the insertion loss of a typical large value wire or foil inductor - even with 12AWG wire size - approached a DC resistance of 0.5 ohms. This means that 10% of the power to the woofer is dissipated by the inductor.
I have always wanted to try a high-power toroid coil since the DC resistance in these inductors is about 1/10th that of any other coil type and now seemed like a good time to give it a go. I also wanted to lower the crossover point from 850Hz to 500Hz , a much better upper-frequency limit for a 12" driver. With a quick check to Parts Express, I found a 3.3mH toroid that with a bit of unwinding would work in my crossover network.
Now unwinding this type of inductor is not as simple as measuring it with an inexpensive RLC meter. Because of the low DCR, higher currents are required to accurately determine the value and so I drug out my oscilloscope, sine wave generator, and a known value capacitor and resistor. It took about 11 turns off of this inductor to get it to the value I needed as determined by the LC tank circuit it created (carefully measure the minimum "null" and read the frequency, then simple math tells you the value).
Back to the TOSLINK/RCA (aka Burr-Brown/ESS Sabre32 Reference) dilemma. Now that the LF extension and clarity is better, I hoped to hear more differences and be able to easily discern them. The large organ recorded by 2-L on the Kare Nordstoga improvisation proved to be the right choice.
All throughout this 24/96 piece (also available in SACD), wall-rattling bass can be heard that captures the true character of a very large brass pipe. Through the Burr-Brown/TOSLINK version, the bass was present but not full nor did it reveal the true timbre of the largest ranks. Sounding muted rather than forward, this configuration - although pleasant - just did not compare to the OPPO/RCA version. The OPPO extracted more information from the source and left you feeling more like "you were there" listening in a pew somewhere forward of the pipes in the balcony. More depth, more width, and more height all combined to giving a well deserved and decisive advantage to the OPPO/RCA version. While other parts of the frequency spectrum were also different, these differences were not as noticeable nor as obvious as the very deep bass and hall ambience.
As I have mentioned in the past, if you are searching for ways to improve your system, look at the size and shape of the sound stage and then choose what sounds more realistic. For now, I will stick with the OPPO/RCA combo for decoding.