Are you sure they supplied you M35 ones?
When I got mine, I requested softer springs & was told they would not supply anything more than 2kg/mm different from standard - I suppose so the shocks & springs were still 'matched'.
I'm having trouble remembering what the standard rates are (12 & 10?), but if so mine are 10 & 8.
8 & 6 sounds too soft, unless they did some changes to the shocks.
BTW, other manufacturers supply 5 - 6 kg/mm springs, so could be OK, even very nice, if shocks valved to suit.
Interested to hear what you think when they're in.