one more thing > + and - of both methods
there no diferences ( in theory) between the electrical method or the optical methode as far as the quality of the sound you will get
the major difference is that since it is a metallic cable, the RCA (electrical) method could be vulnerable to a source of interference and the cable may act as an antenna, picking up stuff that could add up to the data treams and though dropping a (data) bit here a (data) bit there and corrupt the data signal if the cable is too long...
on the other hand, the fiber optic uses light and doesn t care much about being to close to a monitor computer a receiving a massive dose of EMF from a nuclear explosion near by... and can be as long as you want but...
RCA cable are very strong and you can put them anywhere without thinking too much about them ( although you should always respect everything you buy by taking great care..)
fiber optical cables are very fragile. forget about bending them..
since i don t know what the sager sp/dif output is ( electrical/coaxial or optical ) you will have to get whatever the Sager output is..( but based on the look on those pictures, it looks like an optical too me)