What's First, Interconnects or Speaker?

Longer lengths are specified for spdif (coax) cables. Does the same hold forth for optical (toslink) cables?

No. The principles which make a 1.5+ meter length optimal for spdif coax cables are not applicable to optical cables.

Which is not to say that length won't make a difference with optical cables, but I have no particular knowledge of the factors that would be involved.

Best regards,
-- Al

While there is obviously no universally applicable answer, and while obviously technical factors cannot provide a complete answer, I suggest that you take the following into consideration:

1)For line-level analog interconnects, the higher the output impedance of the component driving the cable, the more significant cable differences are likely to be.

2)The lower the nominal impedance of the speaker, the more significant speaker cable differences are likely to be.

3)The greater the variation of speaker impedance with frequency, the more significant speaker cable differences are likely to be.

4)The more critical damping factor and woofer control is to the particular speaker, the more significant speaker cable differences are likely to be.

5)Obviously, phono cables will tend to be fairly critical due to the low signal levels which they conduct.

6)Digital cable differences will increase considerably if length is less than 1.5 meters, and in general digital cables should be 1.5 meters or longer. That is discussed in a number of previous threads, and in this reference.

Of course, differences being "more significant," or the cable being "more critical," does not necessarily mean that a more expensive cable will outperform a less expensive cable in any given system.

Regards,
-- Al