Thoft - I've been messing with the 3.6s for the past few months. I consider their stock components highly optimized and am therefore investigating other upgrades in priority over component upgrades. That said, there are ongoing DIY upgrades happening behind the curtain on this forum - perhaps someone might comment.
I can recommend the fruits of our research, which lands on replacing series feed caps with ClarityCap CSAs in the highest voltage you can fit or afford. Swap resistors to Mills MRA-12s, especially in feed stations.
As background, I have bragged about those yellow caps as state of the art, and they were in their day - tin foil on styrene film, they measure and sound quite good. However CC's CSA invention replaces the normal zinc spluttered end caps with a copper-containing matrix, and updates the geometry to wider and shorter, for a significant performance upgrade. BTW, I've compared the CSAs and CMRs to many of the sexy caps out there, and I believe the CCs are as good as it gets in terms of truth and accuracy, especially at their affordable prices.
Another nearly free upgrade you can DIY is to re-mount the crossover panels on rubber standoffs to reduce vibration in the crossovers.
