Convert XLR to TRS Headphone Cable Issue

My headphone's cable is hardwired with a male TRS termination to the headphone amp.  My new headphone amp (Musical Fidelity) has a combination output jack, either TRS or 3-pin XLR will fit .  I had a 3 wire (cable) 8' extension cable made that is terminated female TRS to connect with the headphone cable and XLR to plug into the amp/out fixture.  So, without the extension I got great music and very good soundstaging with the TRS headphone cable, but with the extension I lost the sound staging, sounds mono.  My headphone amp is "fully balanced"; however,  signal input is not balanced, but is by very good RCA interconnects from my CD player, if that matters...the maker of the cable is very aware of making sure the 3 wires connecting the XLR to the TRS are properly matched, but I cannot visually confirm unless I remove his shrink wrap.  I am not an electrical engineer by any means, but would appreciate thoughts and recommendations.