I will certainly double check it. However I did follow the Gigabyte pinout instructions which for AC97 says r-out on pin 5, and l-out on pin 9 - -excluding the mic for a moment - nothing else.
On the Silverstone card reader the cabling for both AC97 and HD are as two all-in-one plugs, ie no simple options to change - in this case the r-ret, l-ret and gnd are also connected.
Having tried both originally, plus the number (or volume) of posts on front plug issues I think there must be a systems/driver issue here.
Thank you its always appreciated when folks provide suggestions.