I agree on the fact that lcd4 is decent but not the best with the iha6. When I was purchasing headphones and testing it at the shop, I compared with direct from TT, amp by CDM and amp by Iha6.
The hd800s is best from direct from TT
The he1000 was best from iha6
The lcd4 sounded best from cdm (the shop owner felt it's different but not better)
The abyss is better from iha6
I don't have access to a even better amp so maybe when one day I do and have another of the flagships at home, I'll compare again (sold my hd800s since the abyss felt quite some bit better)
The hd800s is best from direct from TT
The he1000 was best from iha6
The lcd4 sounded best from cdm (the shop owner felt it's different but not better)
The abyss is better from iha6
I don't have access to a even better amp so maybe when one day I do and have another of the flagships at home, I'll compare again (sold my hd800s since the abyss felt quite some bit better)