There will be around 1 nanosecond (1/10^9) of difference in propagation delay between 1m and 1.5m length interconnects, which is probably not audible to anyone. However the human nature is that each time you put on music you are likely be bothered by the thought that the sound might have been compromised by mixing cables of different length, so I would recommend using identical length for the peace of mind. If you are going to keep them, use the different length for surrounds.
SACD Interconnects
I know this has been discussed before but I need the latest input from the forum. Very simple question. The multi-channel audio output from an SACD player is a digital signal to the amp or prepro or AVR. Correct so far? OK, that being the case, should the 6 interconnects then be digital audio cable and not analog? Digital audio cable has a 75 ohm impedance and is coax construction which is evidently recommended for SACD output. Please comment. Thanks.