Hey man, I just compared the Optical vs. the RCA output from the Cambridge CXC transport, both sound good, but I prefer the RCA to BNC cable over the optical connection, seems to sound fuller and has a better soundstage, not sure how much is down to the cables ( Oehlbach optical cable and Ghent Audio RCA to BNC 75 Ohm cable ) and how much is the connection type. Also not sure if I would get the same result in a blind test, but I think the RCA to BNC cable sounds better. Just my 2 cents... I don’t think you can go wrong with the Belden.
Also compared the 4 filters, with the CD’s I’ve tried I definitely prefered the White ( Incisive neutral ) filter, doesn’t sound too bright to me, just well extended and detailed. I’m using a tube amp, so that may do some high frequency filtering on its own. Haven’t tried high resolution files yet, tried to use a DVD player as a SACD player but can’t get any sound, not sure what I’m doing wrong.